<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:ef77bd71-6b39-4da7-8478-1b42f55d3bc2,g:2dc172ff-1466-47f5-addf-5b3959755d27-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/ConsolidatedBalanceSheets" xlink:type="simple" xlink:href="fsk-20250331.xsd#ConsolidatedBalanceSheets"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/ConsolidatedBalanceSheets" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_9d28d82d-89b3-44d4-b198-cca0353e0944" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_52f7a980-a227-489a-b0a4-274d957de1c3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_9d28d82d-89b3-44d4-b198-cca0353e0944" xlink:to="loc_us-gaap_StatementTable_52f7a980-a227-489a-b0a4-274d957de1c3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationAxis_550d4b2c-519e-4e3b-a68d-8b24c312cffc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_52f7a980-a227-489a-b0a4-274d957de1c3" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationAxis_550d4b2c-519e-4e3b-a68d-8b24c312cffc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationDomain_550d4b2c-519e-4e3b-a68d-8b24c312cffc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationAxis_550d4b2c-519e-4e3b-a68d-8b24c312cffc" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationDomain_550d4b2c-519e-4e3b-a68d-8b24c312cffc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationDomain_4bc884e2-be27-4109-bb20-3aa8b0fc420c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationAxis_550d4b2c-519e-4e3b-a68d-8b24c312cffc" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationDomain_4bc884e2-be27-4109-bb20-3aa8b0fc420c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentUnaffiliatedIssuerMember_25a3dfe0-3271-4a4b-9f93-cba852653042" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentUnaffiliatedIssuerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_4bc884e2-be27-4109-bb20-3aa8b0fc420c" xlink:to="loc_us-gaap_InvestmentUnaffiliatedIssuerMember_25a3dfe0-3271-4a4b-9f93-cba852653042" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember_bdd4ee0e-3a4e-492c-a68a-4e4b73207628" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_4bc884e2-be27-4109-bb20-3aa8b0fc420c" xlink:to="loc_us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember_bdd4ee0e-3a4e-492c-a68a-4e4b73207628" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentAffiliatedIssuerControlledMember_00f8dd58-f9ae-4885-881d-69037dde2992" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentAffiliatedIssuerControlledMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_4bc884e2-be27-4109-bb20-3aa8b0fc420c" xlink:to="loc_us-gaap_InvestmentAffiliatedIssuerControlledMember_00f8dd58-f9ae-4885-881d-69037dde2992" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_705b08f3-0e2e-46b9-ae0f-b094069e9a1d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d28d82d-89b3-44d4-b198-cca0353e0944" xlink:to="loc_us-gaap_AssetsAbstract_705b08f3-0e2e-46b9-ae0f-b094069e9a1d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtFairValue_e539cf3b-5c06-4e85-9deb-e1277a2b5cd3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_705b08f3-0e2e-46b9-ae0f-b094069e9a1d" xlink:to="loc_us-gaap_InvestmentOwnedAtFairValue_e539cf3b-5c06-4e85-9deb-e1277a2b5cd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashNotHeldInForeignCurrency_5f3095ba-1392-44a3-a6f6-14993219458e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashNotHeldInForeignCurrency"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_705b08f3-0e2e-46b9-ae0f-b094069e9a1d" xlink:to="loc_us-gaap_CashNotHeldInForeignCurrency_5f3095ba-1392-44a3-a6f6-14993219458e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashHeldInForeignCurrency_aa8d8218-59f1-48ac-8163-df03979b1dd3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashHeldInForeignCurrency"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_705b08f3-0e2e-46b9-ae0f-b094069e9a1d" xlink:to="loc_us-gaap_CashHeldInForeignCurrency_aa8d8218-59f1-48ac-8163-df03979b1dd3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableInvestmentSale_5aa4afac-04f7-4157-a9a0-000983013696" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReceivableInvestmentSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_705b08f3-0e2e-46b9-ae0f-b094069e9a1d" xlink:to="loc_us-gaap_ReceivableInvestmentSale_5aa4afac-04f7-4157-a9a0-000983013696" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendAndInterestReceivable_dd2f96eb-5694-4524-84b2-0d9216530282" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendAndInterestReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_705b08f3-0e2e-46b9-ae0f-b094069e9a1d" xlink:to="loc_us-gaap_DividendAndInterestReceivable_dd2f96eb-5694-4524-84b2-0d9216530282" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_8dcd3eaa-c17b-4d79-baee-723032e827a9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_705b08f3-0e2e-46b9-ae0f-b094069e9a1d" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_8dcd3eaa-c17b-4d79-baee-723032e827a9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet_d881194f-bbb4-4c87-8847-7473cac8dce1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_705b08f3-0e2e-46b9-ae0f-b094069e9a1d" xlink:to="loc_us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet_d881194f-bbb4-4c87-8847-7473cac8dce1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssets_169d3405-43c9-4f7d-8ecc-b4068c55fa25" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PrepaidExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_705b08f3-0e2e-46b9-ae0f-b094069e9a1d" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssets_169d3405-43c9-4f7d-8ecc-b4068c55fa25" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_a7c2239b-378c-407a-9589-ef07df66771a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_705b08f3-0e2e-46b9-ae0f-b094069e9a1d" xlink:to="loc_us-gaap_Assets_a7c2239b-378c-407a-9589-ef07df66771a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_4693d636-3c09-408c-84c2-3684810ce711" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d28d82d-89b3-44d4-b198-cca0353e0944" xlink:to="loc_us-gaap_LiabilitiesAbstract_4693d636-3c09-408c-84c2-3684810ce711" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PayableInvestmentPurchase_4d48773a-27a5-49e0-af68-e6b798077e91" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PayableInvestmentPurchase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_4693d636-3c09-408c-84c2-3684810ce711" xlink:to="loc_us-gaap_PayableInvestmentPurchase_4d48773a-27a5-49e0-af68-e6b798077e91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_0bf9651f-a114-49d5-abe3-0ae357720c11" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_4693d636-3c09-408c-84c2-3684810ce711" xlink:to="loc_us-gaap_LongTermDebt_0bf9651f-a114-49d5-abe3-0ae357720c11" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_e57a956e-acf9-4670-95f9-5ebf5f4483b8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_4693d636-3c09-408c-84c2-3684810ce711" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_e57a956e-acf9-4670-95f9-5ebf5f4483b8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DistributionPayable_b5289615-f9b3-4ffb-90fd-5bff90a71d54" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DistributionPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_4693d636-3c09-408c-84c2-3684810ce711" xlink:to="loc_us-gaap_DistributionPayable_b5289615-f9b3-4ffb-90fd-5bff90a71d54" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ManagementFeePayable_271d6809-5784-4815-9471-2c41e90fb423" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ManagementFeePayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_4693d636-3c09-408c-84c2-3684810ce711" xlink:to="loc_us-gaap_ManagementFeePayable_271d6809-5784-4815-9471-2c41e90fb423" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncentiveFeePayable_ae0a9a91-04a2-4f15-9e3c-3e9fb54234d9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncentiveFeePayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_4693d636-3c09-408c-84c2-3684810ce711" xlink:to="loc_us-gaap_IncentiveFeePayable_ae0a9a91-04a2-4f15-9e3c-3e9fb54234d9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedProfessionalFeesCurrentAndNoncurrent_013b8675-81a7-4a00-b6e6-b58409592c3e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccruedProfessionalFeesCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_4693d636-3c09-408c-84c2-3684810ce711" xlink:to="loc_us-gaap_AccruedProfessionalFeesCurrentAndNoncurrent_013b8675-81a7-4a00-b6e6-b58409592c3e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrentAndNoncurrent_0a590e85-5913-449b-a463-a962227dfe88" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_4693d636-3c09-408c-84c2-3684810ce711" xlink:to="loc_us-gaap_InterestPayableCurrentAndNoncurrent_0a590e85-5913-449b-a463-a962227dfe88" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAccruedLiabilitiesCurrentAndNoncurrent_6bf1e552-754a-402a-99ae-1a0fda296d4c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherAccruedLiabilitiesCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_4693d636-3c09-408c-84c2-3684810ce711" xlink:to="loc_us-gaap_OtherAccruedLiabilitiesCurrentAndNoncurrent_6bf1e552-754a-402a-99ae-1a0fda296d4c" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_a830353e-a53c-488c-9cac-51f622f5bae5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_4693d636-3c09-408c-84c2-3684810ce711" xlink:to="loc_us-gaap_Liabilities_a830353e-a53c-488c-9cac-51f622f5bae5" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_76eff2a3-3f46-4407-a63d-59f2aab6b2bb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d28d82d-89b3-44d4-b198-cca0353e0944" xlink:to="loc_us-gaap_CommitmentsAndContingencies_76eff2a3-3f46-4407-a63d-59f2aab6b2bb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_7a37dbf9-92fe-4995-90b5-4a8a95779302" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d28d82d-89b3-44d4-b198-cca0353e0944" xlink:to="loc_us-gaap_StockholdersEquityAbstract_7a37dbf9-92fe-4995-90b5-4a8a95779302" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_870bbe4b-8c04-47f8-ace7-ea0607b6d50f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_7a37dbf9-92fe-4995-90b5-4a8a95779302" xlink:to="loc_us-gaap_PreferredStockValue_870bbe4b-8c04-47f8-ace7-ea0607b6d50f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_4a52d548-5509-4344-a8f8-76f9254365e7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_7a37dbf9-92fe-4995-90b5-4a8a95779302" xlink:to="loc_us-gaap_CommonStockValue_4a52d548-5509-4344-a8f8-76f9254365e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_f0ad024a-594e-42db-9ce9-75b5eced355e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_7a37dbf9-92fe-4995-90b5-4a8a95779302" xlink:to="loc_us-gaap_AdditionalPaidInCapital_f0ad024a-594e-42db-9ce9-75b5eced355e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_16c34690-00c6-46a2-a30a-98dbf9d5d4fb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_7a37dbf9-92fe-4995-90b5-4a8a95779302" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_16c34690-00c6-46a2-a30a-98dbf9d5d4fb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_a9fa78f3-57ac-4213-97bb-bf4280f1fcf5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_7a37dbf9-92fe-4995-90b5-4a8a95779302" xlink:to="loc_us-gaap_StockholdersEquity_a9fa78f3-57ac-4213-97bb-bf4280f1fcf5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_4c7083d0-f536-4b61-b2f9-4637db06219d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d28d82d-89b3-44d4-b198-cca0353e0944" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_4c7083d0-f536-4b61-b2f9-4637db06219d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetAssetValuePerShare_d1ba392f-0db4-4c49-bc03-8be801f73996" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetAssetValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9d28d82d-89b3-44d4-b198-cca0353e0944" xlink:to="loc_us-gaap_NetAssetValuePerShare_d1ba392f-0db4-4c49-bc03-8be801f73996" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="fsk-20250331.xsd#ConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/ConsolidatedBalanceSheetsParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_9fba2f8c-4716-4280-8eed-8401f121f5a5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_2d0316df-1dc7-4dec-b02f-4e1b218a21a2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_9fba2f8c-4716-4280-8eed-8401f121f5a5" xlink:to="loc_us-gaap_StatementTable_2d0316df-1dc7-4dec-b02f-4e1b218a21a2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationAxis_6cfbaf64-fb2a-44ec-81f2-d141ca16e2ad" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_2d0316df-1dc7-4dec-b02f-4e1b218a21a2" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationAxis_6cfbaf64-fb2a-44ec-81f2-d141ca16e2ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationDomain_6cfbaf64-fb2a-44ec-81f2-d141ca16e2ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationAxis_6cfbaf64-fb2a-44ec-81f2-d141ca16e2ad" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationDomain_6cfbaf64-fb2a-44ec-81f2-d141ca16e2ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationDomain_347170ff-530f-450f-86b3-74064e5f93a0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationAxis_6cfbaf64-fb2a-44ec-81f2-d141ca16e2ad" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationDomain_347170ff-530f-450f-86b3-74064e5f93a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentUnaffiliatedIssuerMember_78ce2d8c-7085-4189-80cb-22f9cc674f11" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentUnaffiliatedIssuerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_347170ff-530f-450f-86b3-74064e5f93a0" xlink:to="loc_us-gaap_InvestmentUnaffiliatedIssuerMember_78ce2d8c-7085-4189-80cb-22f9cc674f11" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember_ae5f2b20-61ea-4d86-adaf-16169aca327e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_347170ff-530f-450f-86b3-74064e5f93a0" xlink:to="loc_us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember_ae5f2b20-61ea-4d86-adaf-16169aca327e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentAffiliatedIssuerControlledMember_c9bf1ddc-565f-49ad-8884-4c604965d947" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentAffiliatedIssuerControlledMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_347170ff-530f-450f-86b3-74064e5f93a0" xlink:to="loc_us-gaap_InvestmentAffiliatedIssuerControlledMember_c9bf1ddc-565f-49ad-8884-4c604965d947" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_3d120f6d-30fe-4d14-b4b1-a0ef04ed181f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9fba2f8c-4716-4280-8eed-8401f121f5a5" xlink:to="loc_us-gaap_AssetsAbstract_3d120f6d-30fe-4d14-b4b1-a0ef04ed181f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtCost_01c0f5c9-f267-41ed-8bfb-0a97d739d7f4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_3d120f6d-30fe-4d14-b4b1-a0ef04ed181f" xlink:to="loc_us-gaap_InvestmentOwnedAtCost_01c0f5c9-f267-41ed-8bfb-0a97d739d7f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashHeldInForeignCurrencyAcquisitionCost_afac797e-30f6-4832-a502-f846ee392dd8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashHeldInForeignCurrencyAcquisitionCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_3d120f6d-30fe-4d14-b4b1-a0ef04ed181f" xlink:to="loc_us-gaap_CashHeldInForeignCurrencyAcquisitionCost_afac797e-30f6-4832-a502-f846ee392dd8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_a06b964e-1708-4a3a-99f7-5e98921c0383" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9fba2f8c-4716-4280-8eed-8401f121f5a5" xlink:to="loc_us-gaap_LiabilitiesAbstract_a06b964e-1708-4a3a-99f7-5e98921c0383" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_c0b71b9b-6a97-4b8b-87df-ca7dc130f079" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_a06b964e-1708-4a3a-99f7-5e98921c0383" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_c0b71b9b-6a97-4b8b-87df-ca7dc130f079" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_9a9b0fac-6248-45c5-9bec-f5f57bb77170" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_9fba2f8c-4716-4280-8eed-8401f121f5a5" xlink:to="loc_us-gaap_StockholdersEquityAbstract_9a9b0fac-6248-45c5-9bec-f5f57bb77170" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_b01cab93-b1b9-43a8-9046-698800a63ae6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9a9b0fac-6248-45c5-9bec-f5f57bb77170" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_b01cab93-b1b9-43a8-9046-698800a63ae6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_4beb4d89-684b-4498-9e1a-b9535b3c2471" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9a9b0fac-6248-45c5-9bec-f5f57bb77170" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_4beb4d89-684b-4498-9e1a-b9535b3c2471" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_b6c64a8a-3366-498d-8346-25fbd4951dfd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9a9b0fac-6248-45c5-9bec-f5f57bb77170" xlink:to="loc_us-gaap_PreferredStockSharesIssued_b6c64a8a-3366-498d-8346-25fbd4951dfd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_d06cc668-0129-425e-a8c1-8ff4914c7c64" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9a9b0fac-6248-45c5-9bec-f5f57bb77170" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_d06cc668-0129-425e-a8c1-8ff4914c7c64" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_bd0eca76-5566-4eab-9cf1-e4b7529db7b6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9a9b0fac-6248-45c5-9bec-f5f57bb77170" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_bd0eca76-5566-4eab-9cf1-e4b7529db7b6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_43d849fb-5948-4014-ae9f-7848da1d7346" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9a9b0fac-6248-45c5-9bec-f5f57bb77170" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_43d849fb-5948-4014-ae9f-7848da1d7346" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_8adeff64-f7a1-4049-b375-76a4e51b0c23" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9a9b0fac-6248-45c5-9bec-f5f57bb77170" xlink:to="loc_us-gaap_CommonStockSharesIssued_8adeff64-f7a1-4049-b375-76a4e51b0c23" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_ab4e37a9-5241-49bf-a19f-1a9314c377a8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9a9b0fac-6248-45c5-9bec-f5f57bb77170" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_ab4e37a9-5241-49bf-a19f-1a9314c377a8" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/UnauditedConsolidatedStatementsofOperations" xlink:type="simple" xlink:href="fsk-20250331.xsd#UnauditedConsolidatedStatementsofOperations"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/UnauditedConsolidatedStatementsofOperations" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_e744137b-140a-4077-9253-f91176133adb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_1b757ff4-c6a2-45a8-b093-c82e1512c22d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_e744137b-140a-4077-9253-f91176133adb" xlink:to="loc_us-gaap_StatementTable_1b757ff4-c6a2-45a8-b093-c82e1512c22d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationAxis_edc40eb2-56e0-401b-8317-9df3f1a5efe7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_1b757ff4-c6a2-45a8-b093-c82e1512c22d" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationAxis_edc40eb2-56e0-401b-8317-9df3f1a5efe7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationDomain_edc40eb2-56e0-401b-8317-9df3f1a5efe7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationAxis_edc40eb2-56e0-401b-8317-9df3f1a5efe7" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationDomain_edc40eb2-56e0-401b-8317-9df3f1a5efe7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationDomain_53fedcac-ed3c-46f1-82b3-6fab60b6e2c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationAxis_edc40eb2-56e0-401b-8317-9df3f1a5efe7" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationDomain_53fedcac-ed3c-46f1-82b3-6fab60b6e2c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentUnaffiliatedIssuerMember_f47cf837-3394-47e1-836f-f5c142838cdd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentUnaffiliatedIssuerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_53fedcac-ed3c-46f1-82b3-6fab60b6e2c5" xlink:to="loc_us-gaap_InvestmentUnaffiliatedIssuerMember_f47cf837-3394-47e1-836f-f5c142838cdd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember_a0048fbe-aa88-4a79-86fc-9546b39dda32" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_53fedcac-ed3c-46f1-82b3-6fab60b6e2c5" xlink:to="loc_us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember_a0048fbe-aa88-4a79-86fc-9546b39dda32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentAffiliatedIssuerControlledMember_45eed051-d3ba-4174-b4c4-f6f487d30e26" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentAffiliatedIssuerControlledMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_53fedcac-ed3c-46f1-82b3-6fab60b6e2c5" xlink:to="loc_us-gaap_InvestmentAffiliatedIssuerControlledMember_45eed051-d3ba-4174-b4c4-f6f487d30e26" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_f7142ce6-8327-43b8-aae7-8e1b436b2352" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e744137b-140a-4077-9253-f91176133adb" xlink:to="loc_us-gaap_RevenuesAbstract_f7142ce6-8327-43b8-aae7-8e1b436b2352" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeOperatingPaidInCash_030396a1-c5c1-49e5-b83f-6547268726d3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestIncomeOperatingPaidInCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_f7142ce6-8327-43b8-aae7-8e1b436b2352" xlink:to="loc_us-gaap_InterestIncomeOperatingPaidInCash_030396a1-c5c1-49e5-b83f-6547268726d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeOperatingPaidInKind_9f011d20-b2cd-4ba0-a644-a1aac6e0a160" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestIncomeOperatingPaidInKind"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_f7142ce6-8327-43b8-aae7-8e1b436b2352" xlink:to="loc_us-gaap_InterestIncomeOperatingPaidInKind_9f011d20-b2cd-4ba0-a644-a1aac6e0a160" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FeeIncome_219bc855-ccbe-4949-9c0e-e0cd7ec27dd3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FeeIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_f7142ce6-8327-43b8-aae7-8e1b436b2352" xlink:to="loc_us-gaap_FeeIncome_219bc855-ccbe-4949-9c0e-e0cd7ec27dd3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendIncomeOperating_5a739878-778c-4b7c-8304-48a6c2ea7a8a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_f7142ce6-8327-43b8-aae7-8e1b436b2352" xlink:to="loc_us-gaap_DividendIncomeOperating_5a739878-778c-4b7c-8304-48a6c2ea7a8a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossInvestmentIncomeOperating_cf8593ab-ef90-48c6-9513-adc1d76ee179" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GrossInvestmentIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_f7142ce6-8327-43b8-aae7-8e1b436b2352" xlink:to="loc_us-gaap_GrossInvestmentIncomeOperating_cf8593ab-ef90-48c6-9513-adc1d76ee179" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_b96f8bbb-6bb8-445d-bf25-a974bf176456" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e744137b-140a-4077-9253-f91176133adb" xlink:to="loc_us-gaap_OperatingExpensesAbstract_b96f8bbb-6bb8-445d-bf25-a974bf176456" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ManagementFeeExpense_d88800ff-55cb-4a26-a00e-6a817c6133f5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ManagementFeeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_b96f8bbb-6bb8-445d-bf25-a974bf176456" xlink:to="loc_us-gaap_ManagementFeeExpense_d88800ff-55cb-4a26-a00e-6a817c6133f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncentiveFeeExpense_f1c28a83-4634-4559-8b47-281922b05694" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncentiveFeeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_b96f8bbb-6bb8-445d-bf25-a974bf176456" xlink:to="loc_us-gaap_IncentiveFeeExpense_f1c28a83-4634-4559-8b47-281922b05694" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfessionalFees_1835ddba-a345-476c-a073-b275eb575d46" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProfessionalFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_b96f8bbb-6bb8-445d-bf25-a974bf176456" xlink:to="loc_us-gaap_ProfessionalFees_1835ddba-a345-476c-a073-b275eb575d46" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdministrativeFeesExpense_4bff786d-3c02-4163-b0c2-625d014230f2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdministrativeFeesExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_b96f8bbb-6bb8-445d-bf25-a974bf176456" xlink:to="loc_us-gaap_AdministrativeFeesExpense_4bff786d-3c02-4163-b0c2-625d014230f2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseOperating_367302dd-a42d-4954-ac09-c08bbe83282a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_b96f8bbb-6bb8-445d-bf25-a974bf176456" xlink:to="loc_us-gaap_InterestExpenseOperating_367302dd-a42d-4954-ac09-c08bbe83282a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherGeneralAndAdministrativeExpense_b1241ab6-803c-4dfa-b207-8f3dc6e8d0b5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_b96f8bbb-6bb8-445d-bf25-a974bf176456" xlink:to="loc_us-gaap_OtherGeneralAndAdministrativeExpense_b1241ab6-803c-4dfa-b207-8f3dc6e8d0b5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInvestmentExpense_c9613245-88db-4e14-b984-077e208b73e0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIncomeInvestmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_b96f8bbb-6bb8-445d-bf25-a974bf176456" xlink:to="loc_us-gaap_InvestmentIncomeInvestmentExpense_c9613245-88db-4e14-b984-077e208b73e0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeOperatingAfterExpenseAndTax_d0c00682-5b4e-48b0-91b9-7d508519fd83" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIncomeOperatingAfterExpenseAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e744137b-140a-4077-9253-f91176133adb" xlink:to="loc_us-gaap_InvestmentIncomeOperatingAfterExpenseAndTax_d0c00682-5b4e-48b0-91b9-7d508519fd83" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealizedGainLossInvestmentAndDerivativeOperatingBeforeTaxAbstract_44228213-4a3c-4d39-9146-07fa24d66e4e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RealizedGainLossInvestmentAndDerivativeOperatingBeforeTaxAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e744137b-140a-4077-9253-f91176133adb" xlink:to="loc_us-gaap_RealizedGainLossInvestmentAndDerivativeOperatingBeforeTaxAbstract_44228213-4a3c-4d39-9146-07fa24d66e4e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndEquitySecuritiesRealizedGainLoss_f11cc6ea-b901-4f48-8239-d6ffc50c47f9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtAndEquitySecuritiesRealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealizedGainLossInvestmentAndDerivativeOperatingBeforeTaxAbstract_44228213-4a3c-4d39-9146-07fa24d66e4e" xlink:to="loc_us-gaap_DebtAndEquitySecuritiesRealizedGainLoss_f11cc6ea-b901-4f48-8239-d6ffc50c47f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfDerivatives_fcc6fd26-42bd-452f-8a25-8a39fae2bb7a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GainLossOnSaleOfDerivatives"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealizedGainLossInvestmentAndDerivativeOperatingBeforeTaxAbstract_44228213-4a3c-4d39-9146-07fa24d66e4e" xlink:to="loc_us-gaap_GainLossOnSaleOfDerivatives_fcc6fd26-42bd-452f-8a25-8a39fae2bb7a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossRealized_67451c5c-59ae-4d86-a8af-1ab1aaf87062" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ForeignCurrencyTransactionGainLossRealized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealizedGainLossInvestmentAndDerivativeOperatingBeforeTaxAbstract_44228213-4a3c-4d39-9146-07fa24d66e4e" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossRealized_67451c5c-59ae-4d86-a8af-1ab1aaf87062" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss_38ca8117-666b-40fe-afd4-ca6ff01cd2e7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealizedGainLossInvestmentAndDerivativeOperatingBeforeTaxAbstract_44228213-4a3c-4d39-9146-07fa24d66e4e" xlink:to="loc_us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss_38ca8117-666b-40fe-afd4-ca6ff01cd2e7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnDerivatives_17161d16-ac05-4765-bb33-fe396ecddb0b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnrealizedGainLossOnDerivatives"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealizedGainLossInvestmentAndDerivativeOperatingBeforeTaxAbstract_44228213-4a3c-4d39-9146-07fa24d66e4e" xlink:to="loc_us-gaap_UnrealizedGainLossOnDerivatives_17161d16-ac05-4765-bb33-fe396ecddb0b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossUnrealized_76c1c634-85c7-4814-a330-2a8b8bf7177b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ForeignCurrencyTransactionGainLossUnrealized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealizedGainLossInvestmentAndDerivativeOperatingBeforeTaxAbstract_44228213-4a3c-4d39-9146-07fa24d66e4e" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossUnrealized_76c1c634-85c7-4814-a330-2a8b8bf7177b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_RealizedAndUnrealizedGainLossInvestmentDerivativeAndForeignCurrencyTransactionBeforeTax_87a67ee1-c97a-4111-b714-effa18bcaec3" xlink:href="fsk-20250331.xsd#fsk_RealizedAndUnrealizedGainLossInvestmentDerivativeAndForeignCurrencyTransactionBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RealizedGainLossInvestmentAndDerivativeOperatingBeforeTaxAbstract_44228213-4a3c-4d39-9146-07fa24d66e4e" xlink:to="loc_fsk_RealizedAndUnrealizedGainLossInvestmentDerivativeAndForeignCurrencyTransactionBeforeTax_87a67ee1-c97a-4111-b714-effa18bcaec3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_4bceb32d-6c19-4f7a-8171-24aafb7a848b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e744137b-140a-4077-9253-f91176133adb" xlink:to="loc_us-gaap_NetIncomeLoss_4bceb32d-6c19-4f7a-8171-24aafb7a848b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_04c32179-77b7-47e7-b640-bf66b6465a1b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e744137b-140a-4077-9253-f91176133adb" xlink:to="loc_us-gaap_EarningsPerShareAbstract_04c32179-77b7-47e7-b640-bf66b6465a1b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_06c820a2-2d93-4f66-972a-6e0015f9b1c9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_04c32179-77b7-47e7-b640-bf66b6465a1b" xlink:to="loc_us-gaap_EarningsPerShareBasic_06c820a2-2d93-4f66-972a-6e0015f9b1c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_e9d8f2ca-6ed0-4b01-9b09-e4a3e7614dd4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_04c32179-77b7-47e7-b640-bf66b6465a1b" xlink:to="loc_us-gaap_EarningsPerShareDiluted_e9d8f2ca-6ed0-4b01-9b09-e4a3e7614dd4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_1698e92c-036c-43c5-bbd5-b11d423fbdc5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_04c32179-77b7-47e7-b640-bf66b6465a1b" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_1698e92c-036c-43c5-bbd5-b11d423fbdc5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_faff04c4-49db-4b67-82bf-22e53a4ca01d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_04c32179-77b7-47e7-b640-bf66b6465a1b" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_faff04c4-49db-4b67-82bf-22e53a4ca01d" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/UnauditedConsolidatedScheduleofInvestments" xlink:type="simple" xlink:href="fsk-20250331.xsd#UnauditedConsolidatedScheduleofInvestments"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/UnauditedConsolidatedScheduleofInvestments" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_6d139c47-9119-4b84-82e2-c2de0fa1d3f4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_StatementTable_6d139c47-9119-4b84-82e2-c2de0fa1d3f4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIdentifierAxis_d3d629b5-bc66-4b45-a55b-cc0697df3dae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIdentifierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_6d139c47-9119-4b84-82e2-c2de0fa1d3f4" xlink:to="loc_us-gaap_InvestmentIdentifierAxis_d3d629b5-bc66-4b45-a55b-cc0697df3dae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_99afabfb-7a58-476e-9ded-b1732d749f99" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_6d139c47-9119-4b84-82e2-c2de0fa1d3f4" xlink:to="loc_srt_RangeAxis_99afabfb-7a58-476e-9ded-b1732d749f99" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_99afabfb-7a58-476e-9ded-b1732d749f99_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_99afabfb-7a58-476e-9ded-b1732d749f99" xlink:to="loc_srt_RangeMember_99afabfb-7a58-476e-9ded-b1732d749f99_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_bb9cefb0-5116-487e-8f27-492bf0102662" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_99afabfb-7a58-476e-9ded-b1732d749f99" xlink:to="loc_srt_RangeMember_bb9cefb0-5116-487e-8f27-492bf0102662" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_5fca70ad-4dbd-41f3-bbed-34b71971ad29" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_bb9cefb0-5116-487e-8f27-492bf0102662" xlink:to="loc_srt_MaximumMember_5fca70ad-4dbd-41f3-bbed-34b71971ad29" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_df5fe8da-e16d-4cc4-aa96-660cbe5947ff" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_bb9cefb0-5116-487e-8f27-492bf0102662" xlink:to="loc_srt_MinimumMember_df5fe8da-e16d-4cc4-aa96-660cbe5947ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_4d13e89c-8e2e-474f-b741-6da376b0066e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_6d139c47-9119-4b84-82e2-c2de0fa1d3f4" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_4d13e89c-8e2e-474f-b741-6da376b0066e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_4d13e89c-8e2e-474f-b741-6da376b0066e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_4d13e89c-8e2e-474f-b741-6da376b0066e" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_4d13e89c-8e2e-474f-b741-6da376b0066e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_4d13e89c-8e2e-474f-b741-6da376b0066e" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SeniorSecuredLoansFirstLienMember_4b7891c0-354f-4f12-b808-ced826c008dc" xlink:href="fsk-20250331.xsd#fsk_SeniorSecuredLoansFirstLienMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_SeniorSecuredLoansFirstLienMember_4b7891c0-354f-4f12-b808-ced826c008dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_FundedSeniorSecuredLoansFirstLienMember_52b32c28-9836-4269-96cc-9db31a181519" xlink:href="fsk-20250331.xsd#fsk_FundedSeniorSecuredLoansFirstLienMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_FundedSeniorSecuredLoansFirstLienMember_52b32c28-9836-4269-96cc-9db31a181519" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_UnfundedSeniorSecuredLoansFirstLienMember_4ee8b89f-9ff0-4302-9a63-ab371aadcccb" xlink:href="fsk-20250331.xsd#fsk_UnfundedSeniorSecuredLoansFirstLienMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_UnfundedSeniorSecuredLoansFirstLienMember_4ee8b89f-9ff0-4302-9a63-ab371aadcccb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SeniorSecuredLoansSecondLienMember_486e8db7-d306-4c19-bb58-3f5461b5cf67" xlink:href="fsk-20250331.xsd#fsk_SeniorSecuredLoansSecondLienMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_SeniorSecuredLoansSecondLienMember_486e8db7-d306-4c19-bb58-3f5461b5cf67" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_FundedSeniorSecuredLoansSecondLienMember_00e33dab-631a-4b08-9e0b-4d16bf090fdb" xlink:href="fsk-20250331.xsd#fsk_FundedSeniorSecuredLoansSecondLienMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_FundedSeniorSecuredLoansSecondLienMember_00e33dab-631a-4b08-9e0b-4d16bf090fdb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_OtherSeniorSecuredDebtMember_b3fff76c-8e9d-4b8d-8252-b0f5d6b37e14" xlink:href="fsk-20250331.xsd#fsk_OtherSeniorSecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_OtherSeniorSecuredDebtMember_b3fff76c-8e9d-4b8d-8252-b0f5d6b37e14" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedDebtMember_a1343f42-e06c-442d-a9e4-542d4365814d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubordinatedDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_us-gaap_SubordinatedDebtMember_a1343f42-e06c-442d-a9e4-542d4365814d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_FundedSubordinatedDebtMember_a99bc542-51ed-41f7-81be-86821103f5e2" xlink:href="fsk-20250331.xsd#fsk_FundedSubordinatedDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_FundedSubordinatedDebtMember_a99bc542-51ed-41f7-81be-86821103f5e2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AssetBasedFinanceMember_e6463965-3c0b-4fa9-897c-4366154e4a19" xlink:href="fsk-20250331.xsd#fsk_AssetBasedFinanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_AssetBasedFinanceMember_e6463965-3c0b-4fa9-897c-4366154e4a19" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_FundedAssetBasedFinanceMember_9ca66f66-71f0-4016-b6ba-0f30436b4806" xlink:href="fsk-20250331.xsd#fsk_FundedAssetBasedFinanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_FundedAssetBasedFinanceMember_9ca66f66-71f0-4016-b6ba-0f30436b4806" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_1dfd606c-ce9b-4852-9ae4-d925d1832786" xlink:href="fsk-20250331.xsd#fsk_CreditOpportunitiesPartnersJVLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_1dfd606c-ce9b-4852-9ae4-d925d1832786" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_EquityAndOtherSecuritiesMember_f1c819f2-3040-4176-a39a-e57a8387f1f5" xlink:href="fsk-20250331.xsd#fsk_EquityAndOtherSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_EquityAndOtherSecuritiesMember_f1c819f2-3040-4176-a39a-e57a8387f1f5" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_UnfundedEquityOtherCommitmentsMember_9d9e81d5-29f4-45fe-a96c-81ea556411de" xlink:href="fsk-20250331.xsd#fsk_UnfundedEquityOtherCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_UnfundedEquityOtherCommitmentsMember_9d9e81d5-29f4-45fe-a96c-81ea556411de" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_baa73b0a-abc5-4671-955b-7bb516cbf51c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_us-gaap_EquitySecuritiesMember_baa73b0a-abc5-4671-955b-7bb516cbf51c" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_UnfundedSeniorSecuredLoansSecondLienNettingMember_293027e0-2853-4ab2-936b-bcdcd3e84ef4" xlink:href="fsk-20250331.xsd#fsk_UnfundedSeniorSecuredLoansSecondLienNettingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_UnfundedSeniorSecuredLoansSecondLienNettingMember_293027e0-2853-4ab2-936b-bcdcd3e84ef4" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_UnfundedAssetBasedFinanceNettingMember_3455d032-59d7-4ea4-a6bc-28f6d957e698" xlink:href="fsk-20250331.xsd#fsk_UnfundedAssetBasedFinanceNettingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_UnfundedAssetBasedFinanceNettingMember_3455d032-59d7-4ea4-a6bc-28f6d957e698" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedPercentOfNetAssets_7df91cdd-3a7f-4366-8cd5-487dee6e7a95" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedPercentOfNetAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentOwnedPercentOfNetAssets_7df91cdd-3a7f-4366-8cd5-487dee6e7a95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentInterestRate_a14323b9-67e7-4eaa-b834-25a7592984e9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentInterestRate_a14323b9-67e7-4eaa-b834-25a7592984e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentBasisSpreadVariableRate_177f775f-9e32-430c-bf09-372090e12f80" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentBasisSpreadVariableRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentBasisSpreadVariableRate_177f775f-9e32-430c-bf09-372090e12f80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentInterestRatePaidInKind_f94407f5-7d2a-4290-9fd2-a05a61e35241" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentInterestRatePaidInKind"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentInterestRatePaidInKind_f94407f5-7d2a-4290-9fd2-a05a61e35241" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentInterestRateFloor_cedb2957-d721-4cc0-b9c8-63e075806b38" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentInterestRateFloor"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentInterestRateFloor_cedb2957-d721-4cc0-b9c8-63e075806b38" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedBalancePrincipalAmount_2c38efc4-7a1f-42fa-9f08-78712cfe4427" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedBalancePrincipalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentOwnedBalancePrincipalAmount_2c38efc4-7a1f-42fa-9f08-78712cfe4427" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedBalanceShares_612f6e41-1efa-498c-a825-717313a55674" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedBalanceShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentOwnedBalanceShares_612f6e41-1efa-498c-a825-717313a55674" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtCost_49c5f082-5a95-429b-8654-fdd35fe04c58" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentOwnedAtCost_49c5f082-5a95-429b-8654-fdd35fe04c58" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtFairValue_1152b5cf-2cb2-42b9-b9fb-09a4d58f2915" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentOwnedAtFairValue_1152b5cf-2cb2-42b9-b9fb-09a4d58f2915" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonInvestmentAssetsLessNonInvestmentLiabilitiesPercentOfNetAssets_9645440d-9c41-40b4-b783-c22a49a0ba6a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NonInvestmentAssetsLessNonInvestmentLiabilitiesPercentOfNetAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_NonInvestmentAssetsLessNonInvestmentLiabilitiesPercentOfNetAssets_9645440d-9c41-40b4-b783-c22a49a0ba6a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonInvestmentAssetsLessNonInvestmentLiabilities_2e64fae7-f6a2-4ec5-b4eb-1e5a4f70be89" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NonInvestmentAssetsLessNonInvestmentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_NonInvestmentAssetsLessNonInvestmentLiabilities_2e64fae7-f6a2-4ec5-b4eb-1e5a4f70be89" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNet_8f4b0532-2810-4b97-8939-6315be609ff8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_AssetsNet_8f4b0532-2810-4b97-8939-6315be609ff8" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/UnauditedConsolidatedScheduleofInvestments_1" xlink:type="simple" xlink:href="fsk-20250331.xsd#UnauditedConsolidatedScheduleofInvestments_1"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/UnauditedConsolidatedScheduleofInvestments_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_6d139c47-9119-4b84-82e2-c2de0fa1d3f4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_StatementTable_6d139c47-9119-4b84-82e2-c2de0fa1d3f4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_99afabfb-7a58-476e-9ded-b1732d749f99" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_6d139c47-9119-4b84-82e2-c2de0fa1d3f4" xlink:to="loc_srt_RangeAxis_99afabfb-7a58-476e-9ded-b1732d749f99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_99afabfb-7a58-476e-9ded-b1732d749f99_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_99afabfb-7a58-476e-9ded-b1732d749f99" xlink:to="loc_srt_RangeMember_99afabfb-7a58-476e-9ded-b1732d749f99_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_bb9cefb0-5116-487e-8f27-492bf0102662" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_99afabfb-7a58-476e-9ded-b1732d749f99" xlink:to="loc_srt_RangeMember_bb9cefb0-5116-487e-8f27-492bf0102662" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_5fca70ad-4dbd-41f3-bbed-34b71971ad29" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_bb9cefb0-5116-487e-8f27-492bf0102662" xlink:to="loc_srt_MaximumMember_5fca70ad-4dbd-41f3-bbed-34b71971ad29" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_df5fe8da-e16d-4cc4-aa96-660cbe5947ff" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_bb9cefb0-5116-487e-8f27-492bf0102662" xlink:to="loc_srt_MinimumMember_df5fe8da-e16d-4cc4-aa96-660cbe5947ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_4d13e89c-8e2e-474f-b741-6da376b0066e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_6d139c47-9119-4b84-82e2-c2de0fa1d3f4" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_4d13e89c-8e2e-474f-b741-6da376b0066e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_4d13e89c-8e2e-474f-b741-6da376b0066e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_4d13e89c-8e2e-474f-b741-6da376b0066e" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_4d13e89c-8e2e-474f-b741-6da376b0066e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_4d13e89c-8e2e-474f-b741-6da376b0066e" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SeniorSecuredLoansFirstLienMember_4b7891c0-354f-4f12-b808-ced826c008dc" xlink:href="fsk-20250331.xsd#fsk_SeniorSecuredLoansFirstLienMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_SeniorSecuredLoansFirstLienMember_4b7891c0-354f-4f12-b808-ced826c008dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_FundedSeniorSecuredLoansFirstLienMember_52b32c28-9836-4269-96cc-9db31a181519" xlink:href="fsk-20250331.xsd#fsk_FundedSeniorSecuredLoansFirstLienMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_FundedSeniorSecuredLoansFirstLienMember_52b32c28-9836-4269-96cc-9db31a181519" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_UnfundedSeniorSecuredLoansFirstLienMember_4ee8b89f-9ff0-4302-9a63-ab371aadcccb" xlink:href="fsk-20250331.xsd#fsk_UnfundedSeniorSecuredLoansFirstLienMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_UnfundedSeniorSecuredLoansFirstLienMember_4ee8b89f-9ff0-4302-9a63-ab371aadcccb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SeniorSecuredLoansSecondLienMember_486e8db7-d306-4c19-bb58-3f5461b5cf67" xlink:href="fsk-20250331.xsd#fsk_SeniorSecuredLoansSecondLienMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_SeniorSecuredLoansSecondLienMember_486e8db7-d306-4c19-bb58-3f5461b5cf67" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_FundedSeniorSecuredLoansSecondLienMember_00e33dab-631a-4b08-9e0b-4d16bf090fdb" xlink:href="fsk-20250331.xsd#fsk_FundedSeniorSecuredLoansSecondLienMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_FundedSeniorSecuredLoansSecondLienMember_00e33dab-631a-4b08-9e0b-4d16bf090fdb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_OtherSeniorSecuredDebtMember_b3fff76c-8e9d-4b8d-8252-b0f5d6b37e14" xlink:href="fsk-20250331.xsd#fsk_OtherSeniorSecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_OtherSeniorSecuredDebtMember_b3fff76c-8e9d-4b8d-8252-b0f5d6b37e14" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedDebtMember_a1343f42-e06c-442d-a9e4-542d4365814d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubordinatedDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_us-gaap_SubordinatedDebtMember_a1343f42-e06c-442d-a9e4-542d4365814d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_FundedSubordinatedDebtMember_a99bc542-51ed-41f7-81be-86821103f5e2" xlink:href="fsk-20250331.xsd#fsk_FundedSubordinatedDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_FundedSubordinatedDebtMember_a99bc542-51ed-41f7-81be-86821103f5e2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AssetBasedFinanceMember_e6463965-3c0b-4fa9-897c-4366154e4a19" xlink:href="fsk-20250331.xsd#fsk_AssetBasedFinanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_AssetBasedFinanceMember_e6463965-3c0b-4fa9-897c-4366154e4a19" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_FundedAssetBasedFinanceMember_9ca66f66-71f0-4016-b6ba-0f30436b4806" xlink:href="fsk-20250331.xsd#fsk_FundedAssetBasedFinanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_FundedAssetBasedFinanceMember_9ca66f66-71f0-4016-b6ba-0f30436b4806" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_1dfd606c-ce9b-4852-9ae4-d925d1832786" xlink:href="fsk-20250331.xsd#fsk_CreditOpportunitiesPartnersJVLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_1dfd606c-ce9b-4852-9ae4-d925d1832786" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_EquityAndOtherSecuritiesMember_f1c819f2-3040-4176-a39a-e57a8387f1f5" xlink:href="fsk-20250331.xsd#fsk_EquityAndOtherSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_EquityAndOtherSecuritiesMember_f1c819f2-3040-4176-a39a-e57a8387f1f5" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_UnfundedEquityOtherCommitmentsMember_9d9e81d5-29f4-45fe-a96c-81ea556411de" xlink:href="fsk-20250331.xsd#fsk_UnfundedEquityOtherCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_UnfundedEquityOtherCommitmentsMember_9d9e81d5-29f4-45fe-a96c-81ea556411de" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_baa73b0a-abc5-4671-955b-7bb516cbf51c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_us-gaap_EquitySecuritiesMember_baa73b0a-abc5-4671-955b-7bb516cbf51c" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_UnfundedSeniorSecuredLoansSecondLienNettingMember_293027e0-2853-4ab2-936b-bcdcd3e84ef4" xlink:href="fsk-20250331.xsd#fsk_UnfundedSeniorSecuredLoansSecondLienNettingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_UnfundedSeniorSecuredLoansSecondLienNettingMember_293027e0-2853-4ab2-936b-bcdcd3e84ef4" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_UnfundedAssetBasedFinanceNettingMember_3455d032-59d7-4ea4-a6bc-28f6d957e698" xlink:href="fsk-20250331.xsd#fsk_UnfundedAssetBasedFinanceNettingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_c385e003-599e-415f-a7fd-11a50f82c2e1" xlink:to="loc_fsk_UnfundedAssetBasedFinanceNettingMember_3455d032-59d7-4ea4-a6bc-28f6d957e698" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedPercentOfNetAssets_7df91cdd-3a7f-4366-8cd5-487dee6e7a95" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedPercentOfNetAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentOwnedPercentOfNetAssets_7df91cdd-3a7f-4366-8cd5-487dee6e7a95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentInterestRate_a14323b9-67e7-4eaa-b834-25a7592984e9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentInterestRate_a14323b9-67e7-4eaa-b834-25a7592984e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentBasisSpreadVariableRate_177f775f-9e32-430c-bf09-372090e12f80" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentBasisSpreadVariableRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentBasisSpreadVariableRate_177f775f-9e32-430c-bf09-372090e12f80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentInterestRatePaidInKind_f94407f5-7d2a-4290-9fd2-a05a61e35241" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentInterestRatePaidInKind"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentInterestRatePaidInKind_f94407f5-7d2a-4290-9fd2-a05a61e35241" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentInterestRateFloor_cedb2957-d721-4cc0-b9c8-63e075806b38" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentInterestRateFloor"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentInterestRateFloor_cedb2957-d721-4cc0-b9c8-63e075806b38" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedBalancePrincipalAmount_2c38efc4-7a1f-42fa-9f08-78712cfe4427" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedBalancePrincipalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentOwnedBalancePrincipalAmount_2c38efc4-7a1f-42fa-9f08-78712cfe4427" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedBalanceShares_612f6e41-1efa-498c-a825-717313a55674" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedBalanceShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentOwnedBalanceShares_612f6e41-1efa-498c-a825-717313a55674" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtCost_49c5f082-5a95-429b-8654-fdd35fe04c58" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentOwnedAtCost_49c5f082-5a95-429b-8654-fdd35fe04c58" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtFairValue_1152b5cf-2cb2-42b9-b9fb-09a4d58f2915" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_InvestmentOwnedAtFairValue_1152b5cf-2cb2-42b9-b9fb-09a4d58f2915" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonInvestmentAssetsLessNonInvestmentLiabilitiesPercentOfNetAssets_9645440d-9c41-40b4-b783-c22a49a0ba6a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NonInvestmentAssetsLessNonInvestmentLiabilitiesPercentOfNetAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_NonInvestmentAssetsLessNonInvestmentLiabilitiesPercentOfNetAssets_9645440d-9c41-40b4-b783-c22a49a0ba6a" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonInvestmentAssetsLessNonInvestmentLiabilities_2e64fae7-f6a2-4ec5-b4eb-1e5a4f70be89" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NonInvestmentAssetsLessNonInvestmentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_NonInvestmentAssetsLessNonInvestmentLiabilities_2e64fae7-f6a2-4ec5-b4eb-1e5a4f70be89" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNet_8f4b0532-2810-4b97-8939-6315be609ff8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_abad3ab3-ec3d-4ea5-98f1-eda35b8535b9" xlink:to="loc_us-gaap_AssetsNet_8f4b0532-2810-4b97-8939-6315be609ff8" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/UnauditedConsolidatedScheduleofInvestmentsAdditionalInformation" xlink:type="simple" xlink:href="fsk-20250331.xsd#UnauditedConsolidatedScheduleofInvestmentsAdditionalInformation"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/UnauditedConsolidatedScheduleofInvestmentsAdditionalInformation" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_581f3c1b-77e5-421c-ae7a-aa9ffd4a7a5c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_DerivativeTable_581f3c1b-77e5-421c-ae7a-aa9ffd4a7a5c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OpenForwardForeignCurrencyContractIdentifierAxis_e39fb1f3-f0ae-4244-94a0-939ca50ced31" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OpenForwardForeignCurrencyContractIdentifierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_581f3c1b-77e5-421c-ae7a-aa9ffd4a7a5c" xlink:to="loc_us-gaap_OpenForwardForeignCurrencyContractIdentifierAxis_e39fb1f3-f0ae-4244-94a0-939ca50ced31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_97b99a07-2570-4296-a881-c363cf39cba3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_581f3c1b-77e5-421c-ae7a-aa9ffd4a7a5c" xlink:to="loc_us-gaap_VariableRateAxis_97b99a07-2570-4296-a881-c363cf39cba3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_97b99a07-2570-4296-a881-c363cf39cba3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_97b99a07-2570-4296-a881-c363cf39cba3" xlink:to="loc_us-gaap_VariableRateDomain_97b99a07-2570-4296-a881-c363cf39cba3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_97b99a07-2570-4296-a881-c363cf39cba3" xlink:to="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_LondonInterbankOfferedRateMember_a69f0542-d119-4288-9467-180bddb6e8dc" xlink:href="fsk-20250331.xsd#fsk_LondonInterbankOfferedRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_LondonInterbankOfferedRateMember_a69f0542-d119-4288-9467-180bddb6e8dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_EuroInterbankOfferRateEURIBORMember_6485c1a8-bd18-4d75-a979-e98243bd13ce" xlink:href="fsk-20250331.xsd#fsk_EuroInterbankOfferRateEURIBORMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_EuroInterbankOfferRateEURIBORMember_6485c1a8-bd18-4d75-a979-e98243bd13ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CanadianDollarOfferRateMember_fb3c08d5-8add-4d65-a42e-d051fc76882c" xlink:href="fsk-20250331.xsd#fsk_CanadianDollarOfferRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_CanadianDollarOfferRateMember_fb3c08d5-8add-4d65-a42e-d051fc76882c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_EuroInterbankOfferedRateMember_b84c02e4-9b3b-4a4d-8028-259d6f46ceaf" xlink:href="fsk-20250331.xsd#fsk_EuroInterbankOfferedRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_EuroInterbankOfferedRateMember_b84c02e4-9b3b-4a4d-8028-259d6f46ceaf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AustralianBankBillSwapBidRateMember_844edf2f-d48e-40ae-90dc-b7b8992bbf3f" xlink:href="fsk-20250331.xsd#fsk_AustralianBankBillSwapBidRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_AustralianBankBillSwapBidRateMember_844edf2f-d48e-40ae-90dc-b7b8992bbf3f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AustralianBankBillSwapRateMember_83faae42-7a79-4efa-a4c2-7fd30f3dce1a" xlink:href="fsk-20250331.xsd#fsk_AustralianBankBillSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_AustralianBankBillSwapRateMember_83faae42-7a79-4efa-a4c2-7fd30f3dce1a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_StockholmInterbankOfferedRateMember_4e23d516-9f8a-4f20-b136-a3ca96eb99e3" xlink:href="fsk-20250331.xsd#fsk_StockholmInterbankOfferedRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_StockholmInterbankOfferedRateMember_4e23d516-9f8a-4f20-b136-a3ca96eb99e3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SterlingOvernightIndexAverageMember_99b577c8-05a2-49da-87a6-b68a7353a865" xlink:href="fsk-20250331.xsd#fsk_SterlingOvernightIndexAverageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_SterlingOvernightIndexAverageMember_99b577c8-05a2-49da-87a6-b68a7353a865" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_74e518f9-591a-45fa-b4d2-289d44d868ae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_74e518f9-591a-45fa-b4d2-289d44d868ae" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_af959f8e-99d6-47e7-af2d-cbe436d3265c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_581f3c1b-77e5-421c-ae7a-aa9ffd4a7a5c" xlink:to="loc_us-gaap_InvestmentTypeAxis_af959f8e-99d6-47e7-af2d-cbe436d3265c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_af959f8e-99d6-47e7-af2d-cbe436d3265c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_af959f8e-99d6-47e7-af2d-cbe436d3265c" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_af959f8e-99d6-47e7-af2d-cbe436d3265c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_b0a9a496-7864-42ff-9437-15da8a297abb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_af959f8e-99d6-47e7-af2d-cbe436d3265c" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_b0a9a496-7864-42ff-9437-15da8a297abb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_QualifyingAssetsMember_411aa50c-9c77-4a74-a6d7-bf3c3fb61437" xlink:href="fsk-20250331.xsd#fsk_QualifyingAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_b0a9a496-7864-42ff-9437-15da8a297abb" xlink:to="loc_fsk_QualifyingAssetsMember_411aa50c-9c77-4a74-a6d7-bf3c3fb61437" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetNotionalAmount_54d1d337-1aed-4b12-bf58-303433c6be5c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeAssetNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_DerivativeAssetNotionalAmount_54d1d337-1aed-4b12-bf58-303433c6be5c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_da8e9b73-ae2c-4340-9086-7b0803967306" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_DerivativeNotionalAmount_da8e9b73-ae2c-4340-9086-7b0803967306" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_43a63b2f-9964-4335-9f99-57ee4b9c0148" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_43a63b2f-9964-4335-9f99-57ee4b9c0148" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetFairValueGrossLiability_ec58679b-bdfa-433f-9b15-66820b75d000" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeAssetFairValueGrossLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_DerivativeAssetFairValueGrossLiability_ec58679b-bdfa-433f-9b15-66820b75d000" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_3263b38f-c9dc-4335-926d-9cb68ab1b756" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_DerivativeAssets_3263b38f-c9dc-4335-926d-9cb68ab1b756" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_e75c2542-f757-446a-978e-f2b610068f75" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_DerivativeLiabilities_e75c2542-f757-446a-978e-f2b610068f75" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentVariableRate_4fe8ce6c-8c47-4826-9661-45e6eff176b3" xlink:href="fsk-20250331.xsd#fsk_InvestmentVariableRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_fsk_InvestmentVariableRate_4fe8ce6c-8c47-4826-9661-45e6eff176b3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedPercentOfNetAssets_0a7fe0f6-e4ba-40cc-8314-1dd19b1d86f3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedPercentOfNetAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_InvestmentOwnedPercentOfNetAssets_0a7fe0f6-e4ba-40cc-8314-1dd19b1d86f3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_88b9e68f-6760-418d-be3a-8e6c554479b2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_318b48be-aca3-41bc-b373-45249f8282b1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_88b9e68f-6760-418d-be3a-8e6c554479b2" xlink:to="loc_us-gaap_StatementTable_318b48be-aca3-41bc-b373-45249f8282b1" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIdentifierAxis_2548f1e8-77d2-4ba8-9270-583bb45c60b2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIdentifierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_318b48be-aca3-41bc-b373-45249f8282b1" xlink:to="loc_us-gaap_InvestmentIdentifierAxis_2548f1e8-77d2-4ba8-9270-583bb45c60b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationAxis_2dd3975d-7f95-4918-9311-9ce0cb6167f4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_318b48be-aca3-41bc-b373-45249f8282b1" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationAxis_2dd3975d-7f95-4918-9311-9ce0cb6167f4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationDomain_2dd3975d-7f95-4918-9311-9ce0cb6167f4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationAxis_2dd3975d-7f95-4918-9311-9ce0cb6167f4" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationDomain_2dd3975d-7f95-4918-9311-9ce0cb6167f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationDomain_bcf6b9c9-0862-4dd6-aacd-6dd1290e962e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationAxis_2dd3975d-7f95-4918-9311-9ce0cb6167f4" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationDomain_bcf6b9c9-0862-4dd6-aacd-6dd1290e962e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember_37597f35-61bc-44b4-a237-1bab93a200cc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_bcf6b9c9-0862-4dd6-aacd-6dd1290e962e" xlink:to="loc_us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember_37597f35-61bc-44b4-a237-1bab93a200cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentAffiliatedIssuerControlledMember_05857414-21df-4cac-8c91-dc05d73570de" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentAffiliatedIssuerControlledMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_bcf6b9c9-0862-4dd6-aacd-6dd1290e962e" xlink:to="loc_us-gaap_InvestmentAffiliatedIssuerControlledMember_05857414-21df-4cac-8c91-dc05d73570de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward_2e049e07-3a95-4176-858e-27bb81fd8f8c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_88b9e68f-6760-418d-be3a-8e6c554479b2" xlink:to="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward_2e049e07-3a95-4176-858e-27bb81fd8f8c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtFairValue_a7d4f67f-7b11-4506-9f73-e4a3eb45e5b0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward_2e049e07-3a95-4176-858e-27bb81fd8f8c" xlink:to="loc_us-gaap_InvestmentOwnedAtFairValue_a7d4f67f-7b11-4506-9f73-e4a3eb45e5b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueGrossAdditions_d0214618-53b8-4337-abf0-a4b2bc0517d7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueGrossAdditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward_2e049e07-3a95-4176-858e-27bb81fd8f8c" xlink:to="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueGrossAdditions_d0214618-53b8-4337-abf0-a4b2bc0517d7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueGrossReductions_e98f0207-0c32-492d-92cb-046dfae9e566" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueGrossReductions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward_2e049e07-3a95-4176-858e-27bb81fd8f8c" xlink:to="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueGrossReductions_e98f0207-0c32-492d-92cb-046dfae9e566" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndEquitySecuritiesRealizedGainLoss_7ac2f1de-8de4-4d97-85bb-a51d8332be95" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtAndEquitySecuritiesRealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward_2e049e07-3a95-4176-858e-27bb81fd8f8c" xlink:to="loc_us-gaap_DebtAndEquitySecuritiesRealizedGainLoss_7ac2f1de-8de4-4d97-85bb-a51d8332be95" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss_710767b3-a9a0-4148-84a6-ff9392aa0ebf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward_2e049e07-3a95-4176-858e-27bb81fd8f8c" xlink:to="loc_us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss_710767b3-a9a0-4148-84a6-ff9392aa0ebf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtFairValue_332ef274-20c9-40da-839c-9e542c70c55b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeOperating_4f5ccc2e-ba14-4307-9692-1ace3b3c82c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_88b9e68f-6760-418d-be3a-8e6c554479b2" xlink:to="loc_us-gaap_InterestIncomeOperating_4f5ccc2e-ba14-4307-9692-1ace3b3c82c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeOperatingPaidInKind_1cf23ffe-9d67-4725-af19-b059403bb4d0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestIncomeOperatingPaidInKind"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_88b9e68f-6760-418d-be3a-8e6c554479b2" xlink:to="loc_us-gaap_InterestIncomeOperatingPaidInKind_1cf23ffe-9d67-4725-af19-b059403bb4d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FeeIncome_f7a38b58-a8c2-43c7-81c4-64e7c69cec6c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FeeIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_88b9e68f-6760-418d-be3a-8e6c554479b2" xlink:to="loc_us-gaap_FeeIncome_f7a38b58-a8c2-43c7-81c4-64e7c69cec6c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendIncomeOperating_1f014ed2-bc64-423e-848b-f0bb133207c6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_88b9e68f-6760-418d-be3a-8e6c554479b2" xlink:to="loc_us-gaap_DividendIncomeOperating_1f014ed2-bc64-423e-848b-f0bb133207c6" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/UnauditedConsolidatedScheduleofInvestmentsAdditionalInformation_1" xlink:type="simple" xlink:href="fsk-20250331.xsd#UnauditedConsolidatedScheduleofInvestmentsAdditionalInformation_1"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/UnauditedConsolidatedScheduleofInvestmentsAdditionalInformation_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_581f3c1b-77e5-421c-ae7a-aa9ffd4a7a5c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_DerivativeTable_581f3c1b-77e5-421c-ae7a-aa9ffd4a7a5c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_97b99a07-2570-4296-a881-c363cf39cba3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_581f3c1b-77e5-421c-ae7a-aa9ffd4a7a5c" xlink:to="loc_us-gaap_VariableRateAxis_97b99a07-2570-4296-a881-c363cf39cba3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_97b99a07-2570-4296-a881-c363cf39cba3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_97b99a07-2570-4296-a881-c363cf39cba3" xlink:to="loc_us-gaap_VariableRateDomain_97b99a07-2570-4296-a881-c363cf39cba3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_97b99a07-2570-4296-a881-c363cf39cba3" xlink:to="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_LondonInterbankOfferedRateMember_a69f0542-d119-4288-9467-180bddb6e8dc" xlink:href="fsk-20250331.xsd#fsk_LondonInterbankOfferedRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_LondonInterbankOfferedRateMember_a69f0542-d119-4288-9467-180bddb6e8dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_EuroInterbankOfferRateEURIBORMember_6485c1a8-bd18-4d75-a979-e98243bd13ce" xlink:href="fsk-20250331.xsd#fsk_EuroInterbankOfferRateEURIBORMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_EuroInterbankOfferRateEURIBORMember_6485c1a8-bd18-4d75-a979-e98243bd13ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CanadianDollarOfferRateMember_fb3c08d5-8add-4d65-a42e-d051fc76882c" xlink:href="fsk-20250331.xsd#fsk_CanadianDollarOfferRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_CanadianDollarOfferRateMember_fb3c08d5-8add-4d65-a42e-d051fc76882c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_EuroInterbankOfferedRateMember_b84c02e4-9b3b-4a4d-8028-259d6f46ceaf" xlink:href="fsk-20250331.xsd#fsk_EuroInterbankOfferedRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_EuroInterbankOfferedRateMember_b84c02e4-9b3b-4a4d-8028-259d6f46ceaf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AustralianBankBillSwapBidRateMember_844edf2f-d48e-40ae-90dc-b7b8992bbf3f" xlink:href="fsk-20250331.xsd#fsk_AustralianBankBillSwapBidRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_AustralianBankBillSwapBidRateMember_844edf2f-d48e-40ae-90dc-b7b8992bbf3f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AustralianBankBillSwapRateMember_83faae42-7a79-4efa-a4c2-7fd30f3dce1a" xlink:href="fsk-20250331.xsd#fsk_AustralianBankBillSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_AustralianBankBillSwapRateMember_83faae42-7a79-4efa-a4c2-7fd30f3dce1a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_StockholmInterbankOfferedRateMember_4e23d516-9f8a-4f20-b136-a3ca96eb99e3" xlink:href="fsk-20250331.xsd#fsk_StockholmInterbankOfferedRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_StockholmInterbankOfferedRateMember_4e23d516-9f8a-4f20-b136-a3ca96eb99e3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SterlingOvernightIndexAverageMember_99b577c8-05a2-49da-87a6-b68a7353a865" xlink:href="fsk-20250331.xsd#fsk_SterlingOvernightIndexAverageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_fsk_SterlingOvernightIndexAverageMember_99b577c8-05a2-49da-87a6-b68a7353a865" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_74e518f9-591a-45fa-b4d2-289d44d868ae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_aceb49bd-8281-4193-9b43-4f1d9bc42165" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_74e518f9-591a-45fa-b4d2-289d44d868ae" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_af959f8e-99d6-47e7-af2d-cbe436d3265c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_581f3c1b-77e5-421c-ae7a-aa9ffd4a7a5c" xlink:to="loc_us-gaap_InvestmentTypeAxis_af959f8e-99d6-47e7-af2d-cbe436d3265c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_af959f8e-99d6-47e7-af2d-cbe436d3265c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_af959f8e-99d6-47e7-af2d-cbe436d3265c" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_af959f8e-99d6-47e7-af2d-cbe436d3265c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_b0a9a496-7864-42ff-9437-15da8a297abb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_af959f8e-99d6-47e7-af2d-cbe436d3265c" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_b0a9a496-7864-42ff-9437-15da8a297abb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_QualifyingAssetsMember_411aa50c-9c77-4a74-a6d7-bf3c3fb61437" xlink:href="fsk-20250331.xsd#fsk_QualifyingAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_b0a9a496-7864-42ff-9437-15da8a297abb" xlink:to="loc_fsk_QualifyingAssetsMember_411aa50c-9c77-4a74-a6d7-bf3c3fb61437" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetNotionalAmount_54d1d337-1aed-4b12-bf58-303433c6be5c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeAssetNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_DerivativeAssetNotionalAmount_54d1d337-1aed-4b12-bf58-303433c6be5c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_da8e9b73-ae2c-4340-9086-7b0803967306" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_DerivativeNotionalAmount_da8e9b73-ae2c-4340-9086-7b0803967306" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_43a63b2f-9964-4335-9f99-57ee4b9c0148" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_43a63b2f-9964-4335-9f99-57ee4b9c0148" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetFairValueGrossLiability_ec58679b-bdfa-433f-9b15-66820b75d000" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeAssetFairValueGrossLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_DerivativeAssetFairValueGrossLiability_ec58679b-bdfa-433f-9b15-66820b75d000" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_3263b38f-c9dc-4335-926d-9cb68ab1b756" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_DerivativeAssets_3263b38f-c9dc-4335-926d-9cb68ab1b756" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_e75c2542-f757-446a-978e-f2b610068f75" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_DerivativeLiabilities_e75c2542-f757-446a-978e-f2b610068f75" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentVariableRate_4fe8ce6c-8c47-4826-9661-45e6eff176b3" xlink:href="fsk-20250331.xsd#fsk_InvestmentVariableRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_fsk_InvestmentVariableRate_4fe8ce6c-8c47-4826-9661-45e6eff176b3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedPercentOfNetAssets_0a7fe0f6-e4ba-40cc-8314-1dd19b1d86f3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedPercentOfNetAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_29b2039b-e461-45fc-b4f9-689dd5e1db7c" xlink:to="loc_us-gaap_InvestmentOwnedPercentOfNetAssets_0a7fe0f6-e4ba-40cc-8314-1dd19b1d86f3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_88b9e68f-6760-418d-be3a-8e6c554479b2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_318b48be-aca3-41bc-b373-45249f8282b1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_88b9e68f-6760-418d-be3a-8e6c554479b2" xlink:to="loc_us-gaap_StatementTable_318b48be-aca3-41bc-b373-45249f8282b1" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationAxis_2dd3975d-7f95-4918-9311-9ce0cb6167f4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_318b48be-aca3-41bc-b373-45249f8282b1" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationAxis_2dd3975d-7f95-4918-9311-9ce0cb6167f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationDomain_2dd3975d-7f95-4918-9311-9ce0cb6167f4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationAxis_2dd3975d-7f95-4918-9311-9ce0cb6167f4" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationDomain_2dd3975d-7f95-4918-9311-9ce0cb6167f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationDomain_bcf6b9c9-0862-4dd6-aacd-6dd1290e962e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationAxis_2dd3975d-7f95-4918-9311-9ce0cb6167f4" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationDomain_bcf6b9c9-0862-4dd6-aacd-6dd1290e962e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember_37597f35-61bc-44b4-a237-1bab93a200cc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_bcf6b9c9-0862-4dd6-aacd-6dd1290e962e" xlink:to="loc_us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember_37597f35-61bc-44b4-a237-1bab93a200cc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentAffiliatedIssuerControlledMember_05857414-21df-4cac-8c91-dc05d73570de" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentAffiliatedIssuerControlledMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_bcf6b9c9-0862-4dd6-aacd-6dd1290e962e" xlink:to="loc_us-gaap_InvestmentAffiliatedIssuerControlledMember_05857414-21df-4cac-8c91-dc05d73570de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward_2e049e07-3a95-4176-858e-27bb81fd8f8c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_88b9e68f-6760-418d-be3a-8e6c554479b2" xlink:to="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward_2e049e07-3a95-4176-858e-27bb81fd8f8c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtFairValue_a7d4f67f-7b11-4506-9f73-e4a3eb45e5b0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward_2e049e07-3a95-4176-858e-27bb81fd8f8c" xlink:to="loc_us-gaap_InvestmentOwnedAtFairValue_a7d4f67f-7b11-4506-9f73-e4a3eb45e5b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueGrossAdditions_d0214618-53b8-4337-abf0-a4b2bc0517d7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueGrossAdditions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward_2e049e07-3a95-4176-858e-27bb81fd8f8c" xlink:to="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueGrossAdditions_d0214618-53b8-4337-abf0-a4b2bc0517d7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueGrossReductions_e98f0207-0c32-492d-92cb-046dfae9e566" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueGrossReductions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward_2e049e07-3a95-4176-858e-27bb81fd8f8c" xlink:to="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueGrossReductions_e98f0207-0c32-492d-92cb-046dfae9e566" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndEquitySecuritiesRealizedGainLoss_7ac2f1de-8de4-4d97-85bb-a51d8332be95" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtAndEquitySecuritiesRealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward_2e049e07-3a95-4176-858e-27bb81fd8f8c" xlink:to="loc_us-gaap_DebtAndEquitySecuritiesRealizedGainLoss_7ac2f1de-8de4-4d97-85bb-a51d8332be95" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss_710767b3-a9a0-4148-84a6-ff9392aa0ebf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentsInAndAdvancesToAffiliatesAtFairValueRollForward_2e049e07-3a95-4176-858e-27bb81fd8f8c" xlink:to="loc_us-gaap_DebtAndEquitySecuritiesUnrealizedGainLoss_710767b3-a9a0-4148-84a6-ff9392aa0ebf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtFairValue_332ef274-20c9-40da-839c-9e542c70c55b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeOperating_4f5ccc2e-ba14-4307-9692-1ace3b3c82c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_88b9e68f-6760-418d-be3a-8e6c554479b2" xlink:to="loc_us-gaap_InterestIncomeOperating_4f5ccc2e-ba14-4307-9692-1ace3b3c82c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeOperatingPaidInKind_1cf23ffe-9d67-4725-af19-b059403bb4d0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestIncomeOperatingPaidInKind"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_88b9e68f-6760-418d-be3a-8e6c554479b2" xlink:to="loc_us-gaap_InterestIncomeOperatingPaidInKind_1cf23ffe-9d67-4725-af19-b059403bb4d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FeeIncome_f7a38b58-a8c2-43c7-81c4-64e7c69cec6c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FeeIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_88b9e68f-6760-418d-be3a-8e6c554479b2" xlink:to="loc_us-gaap_FeeIncome_f7a38b58-a8c2-43c7-81c4-64e7c69cec6c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendIncomeOperating_1f014ed2-bc64-423e-848b-f0bb133207c6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_88b9e68f-6760-418d-be3a-8e6c554479b2" xlink:to="loc_us-gaap_DividendIncomeOperating_1f014ed2-bc64-423e-848b-f0bb133207c6" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/UnauditedConsolidatedScheduleofInvestmentsAdditionalInformationInterestRateSwaps" xlink:type="simple" xlink:href="fsk-20250331.xsd#UnauditedConsolidatedScheduleofInvestmentsAdditionalInformationInterestRateSwaps"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/UnauditedConsolidatedScheduleofInvestmentsAdditionalInformationInterestRateSwaps" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_e250a299-e249-4d9a-b5a4-a9dcf62cd1c8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_e417f705-4dd6-4563-bc06-f60029b7951f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_e250a299-e249-4d9a-b5a4-a9dcf62cd1c8" xlink:to="loc_us-gaap_StatementTable_e417f705-4dd6-4563-bc06-f60029b7951f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_d3621a7c-4e77-4aab-b4e6-645dfdb601ff" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_e417f705-4dd6-4563-bc06-f60029b7951f" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_d3621a7c-4e77-4aab-b4e6-645dfdb601ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_d3621a7c-4e77-4aab-b4e6-645dfdb601ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_d3621a7c-4e77-4aab-b4e6-645dfdb601ff" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_d3621a7c-4e77-4aab-b4e6-645dfdb601ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_c39dbd10-e734-4679-955d-13c7d39493b2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_d3621a7c-4e77-4aab-b4e6-645dfdb601ff" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_c39dbd10-e734-4679-955d-13c7d39493b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_01bb4269-e203-49c0-94e3-c4bd663e9e5f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_c39dbd10-e734-4679-955d-13c7d39493b2" xlink:to="loc_us-gaap_InterestRateSwapMember_01bb4269-e203-49c0-94e3-c4bd663e9e5f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InterestRateSwapOneMember_7841cb48-3054-426a-8147-7eac4ced2e94" xlink:href="fsk-20250331.xsd#fsk_InterestRateSwapOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_01bb4269-e203-49c0-94e3-c4bd663e9e5f" xlink:to="loc_fsk_InterestRateSwapOneMember_7841cb48-3054-426a-8147-7eac4ced2e94" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InterestRateSwapTwoMember_bb26502c-4bda-49db-8b9c-e8255f1baa63" xlink:href="fsk-20250331.xsd#fsk_InterestRateSwapTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_01bb4269-e203-49c0-94e3-c4bd663e9e5f" xlink:to="loc_fsk_InterestRateSwapTwoMember_bb26502c-4bda-49db-8b9c-e8255f1baa63" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InterestRateSwapThreeMember_3d5bedce-7ee1-4839-86c6-94996d48489c" xlink:href="fsk-20250331.xsd#fsk_InterestRateSwapThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_01bb4269-e203-49c0-94e3-c4bd663e9e5f" xlink:to="loc_fsk_InterestRateSwapThreeMember_3d5bedce-7ee1-4839-86c6-94996d48489c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InterestRateSwapFourMember_f78abe80-bac3-44aa-b149-93efc5b8e793" xlink:href="fsk-20250331.xsd#fsk_InterestRateSwapFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_01bb4269-e203-49c0-94e3-c4bd663e9e5f" xlink:to="loc_fsk_InterestRateSwapFourMember_f78abe80-bac3-44aa-b149-93efc5b8e793" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFixedInterestRate_f5911a26-d9b6-4c77-a53f-1f351771bc2a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e250a299-e249-4d9a-b5a4-a9dcf62cd1c8" xlink:to="loc_us-gaap_DerivativeFixedInterestRate_f5911a26-d9b6-4c77-a53f-1f351771bc2a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeBasisSpreadOnVariableRate_845f92d4-56a6-4dc4-9113-b2050e48d5af" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeBasisSpreadOnVariableRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e250a299-e249-4d9a-b5a4-a9dcf62cd1c8" xlink:to="loc_us-gaap_DerivativeBasisSpreadOnVariableRate_845f92d4-56a6-4dc4-9113-b2050e48d5af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtCost_f9288541-7b94-4849-a259-473dedb19d0b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e250a299-e249-4d9a-b5a4-a9dcf62cd1c8" xlink:to="loc_us-gaap_InvestmentOwnedAtCost_f9288541-7b94-4849-a259-473dedb19d0b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtFairValue_924e7aea-1246-461d-a5da-02172c58716f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e250a299-e249-4d9a-b5a4-a9dcf62cd1c8" xlink:to="loc_us-gaap_InvestmentOwnedAtFairValue_924e7aea-1246-461d-a5da-02172c58716f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromInvestments_8184b133-8255-4602-ad4f-6ba8a0fafab4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentsForProceedsFromInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e250a299-e249-4d9a-b5a4-a9dcf62cd1c8" xlink:to="loc_us-gaap_PaymentsForProceedsFromInvestments_8184b133-8255-4602-ad4f-6ba8a0fafab4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyDistributableEarningsLossAccumulatedAppreciationDepreciation_99eeee0c-aa38-4439-94bf-369bec16e844" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyDistributableEarningsLossAccumulatedAppreciationDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_e250a299-e249-4d9a-b5a4-a9dcf62cd1c8" xlink:to="loc_us-gaap_InvestmentCompanyDistributableEarningsLossAccumulatedAppreciationDepreciation_99eeee0c-aa38-4439-94bf-369bec16e844" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/SummaryofSignificantAccountingPoliciesDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#SummaryofSignificantAccountingPoliciesDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/SummaryofSignificantAccountingPoliciesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_21625a87-e83a-482a-a711-4b47c97c8325" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_f0870530-24e4-4d88-9937-783929b3af19" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_21625a87-e83a-482a-a711-4b47c97c8325" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_f0870530-24e4-4d88-9937-783929b3af19" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_befd7122-7a8c-487e-9e56-ee474b2ce945" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_f0870530-24e4-4d88-9937-783929b3af19" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_befd7122-7a8c-487e-9e56-ee474b2ce945" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_befd7122-7a8c-487e-9e56-ee474b2ce945_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_befd7122-7a8c-487e-9e56-ee474b2ce945" xlink:to="loc_us-gaap_RelatedPartyDomain_befd7122-7a8c-487e-9e56-ee474b2ce945_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_49764ae3-8fa7-4390-bda3-59f1e641fea9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_befd7122-7a8c-487e-9e56-ee474b2ce945" xlink:to="loc_us-gaap_RelatedPartyDomain_49764ae3-8fa7-4390-bda3-59f1e641fea9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AffiliatedEntityMember_f50c767c-dd4c-4090-847e-2064dc17e95b" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_AffiliatedEntityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_49764ae3-8fa7-4390-bda3-59f1e641fea9" xlink:to="loc_srt_AffiliatedEntityMember_f50c767c-dd4c-4090-847e-2064dc17e95b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_84901af6-ab01-4822-a605-0707dc0223b5" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_f0870530-24e4-4d88-9937-783929b3af19" xlink:to="loc_srt_ProductOrServiceAxis_84901af6-ab01-4822-a605-0707dc0223b5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_84901af6-ab01-4822-a605-0707dc0223b5_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_84901af6-ab01-4822-a605-0707dc0223b5" xlink:to="loc_srt_ProductsAndServicesDomain_84901af6-ab01-4822-a605-0707dc0223b5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_af5797f0-d320-494b-91c8-5590ec10cb14" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_84901af6-ab01-4822-a605-0707dc0223b5" xlink:to="loc_srt_ProductsAndServicesDomain_af5797f0-d320-494b-91c8-5590ec10cb14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_StructuringFeesMember_4b7364ef-023c-4733-babc-ea1e4aaf503f" xlink:href="fsk-20250331.xsd#fsk_StructuringFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_af5797f0-d320-494b-91c8-5590ec10cb14" xlink:to="loc_fsk_StructuringFeesMember_4b7364ef-023c-4733-babc-ea1e4aaf503f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_3aa4b3fb-9f91-474e-9edf-b336aa09c550" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_f0870530-24e4-4d88-9937-783929b3af19" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_3aa4b3fb-9f91-474e-9edf-b336aa09c550" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_3aa4b3fb-9f91-474e-9edf-b336aa09c550_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_3aa4b3fb-9f91-474e-9edf-b336aa09c550" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_3aa4b3fb-9f91-474e-9edf-b336aa09c550_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_de4025c4-b3ce-4d58-8d28-f489f9e4e406" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_3aa4b3fb-9f91-474e-9edf-b336aa09c550" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_de4025c4-b3ce-4d58-8d28-f489f9e4e406" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentAdvisoryAgreementIncentiveRateRealizedCapitalGainsMember_68c5456d-d2b0-4a89-be1c-475270e59532" xlink:href="fsk-20250331.xsd#fsk_InvestmentAdvisoryAgreementIncentiveRateRealizedCapitalGainsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_de4025c4-b3ce-4d58-8d28-f489f9e4e406" xlink:to="loc_fsk_InvestmentAdvisoryAgreementIncentiveRateRealizedCapitalGainsMember_68c5456d-d2b0-4a89-be1c-475270e59532" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentAdvisoryAgreementIncentiveRateQuarterlyInArrearsCatchUpThresholdMember_9d3ecce3-d040-402c-9a54-7b26344df5aa" xlink:href="fsk-20250331.xsd#fsk_InvestmentAdvisoryAgreementIncentiveRateQuarterlyInArrearsCatchUpThresholdMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_de4025c4-b3ce-4d58-8d28-f489f9e4e406" xlink:to="loc_fsk_InvestmentAdvisoryAgreementIncentiveRateQuarterlyInArrearsCatchUpThresholdMember_9d3ecce3-d040-402c-9a54-7b26344df5aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentAdvisoryAgreementIncentiveRateQuarterlyCatchUpThresholdMember_e93f6478-cedb-4a6f-abac-42de2086ead3" xlink:href="fsk-20250331.xsd#fsk_InvestmentAdvisoryAgreementIncentiveRateQuarterlyCatchUpThresholdMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_de4025c4-b3ce-4d58-8d28-f489f9e4e406" xlink:to="loc_fsk_InvestmentAdvisoryAgreementIncentiveRateQuarterlyCatchUpThresholdMember_e93f6478-cedb-4a6f-abac-42de2086ead3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentAdvisoryAgreementIncentiveRateAnnualizedHurdleRateMember_858dcfa2-f46b-46e4-b903-b50213a4e91a" xlink:href="fsk-20250331.xsd#fsk_InvestmentAdvisoryAgreementIncentiveRateAnnualizedHurdleRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_de4025c4-b3ce-4d58-8d28-f489f9e4e406" xlink:to="loc_fsk_InvestmentAdvisoryAgreementIncentiveRateAnnualizedHurdleRateMember_858dcfa2-f46b-46e4-b903-b50213a4e91a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentAdvisoryAgreementIncentiveRatePreIncentiveFeeNetInvestmentIncomeBelowCatchUpThresholdMember_26451769-2b2d-43a0-989c-c09ef45ca10b" xlink:href="fsk-20250331.xsd#fsk_InvestmentAdvisoryAgreementIncentiveRatePreIncentiveFeeNetInvestmentIncomeBelowCatchUpThresholdMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_de4025c4-b3ce-4d58-8d28-f489f9e4e406" xlink:to="loc_fsk_InvestmentAdvisoryAgreementIncentiveRatePreIncentiveFeeNetInvestmentIncomeBelowCatchUpThresholdMember_26451769-2b2d-43a0-989c-c09ef45ca10b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentAdvisoryAgreementIncentiveRateAnnualizedCatchUpThresholdMember_b8b28388-15a0-4394-b927-2b984748e06c" xlink:href="fsk-20250331.xsd#fsk_InvestmentAdvisoryAgreementIncentiveRateAnnualizedCatchUpThresholdMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_de4025c4-b3ce-4d58-8d28-f489f9e4e406" xlink:to="loc_fsk_InvestmentAdvisoryAgreementIncentiveRateAnnualizedCatchUpThresholdMember_b8b28388-15a0-4394-b927-2b984748e06c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ManagementAndServiceFeesIncentiveRate_d56eaf9e-cf76-4878-9e62-039dead5d1d1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ManagementAndServiceFeesIncentiveRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_21625a87-e83a-482a-a711-4b47c97c8325" xlink:to="loc_us-gaap_ManagementAndServiceFeesIncentiveRate_d56eaf9e-cf76-4878-9e62-039dead5d1d1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentBankingAdvisoryBrokerageAndUnderwritingFeesAndCommissions_527b00a9-622a-4bfe-943f-b4c7195e7270" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentBankingAdvisoryBrokerageAndUnderwritingFeesAndCommissions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_21625a87-e83a-482a-a711-4b47c97c8325" xlink:to="loc_us-gaap_InvestmentBankingAdvisoryBrokerageAndUnderwritingFeesAndCommissions_527b00a9-622a-4bfe-943f-b4c7195e7270" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/ShareTransactionsDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#ShareTransactionsDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/ShareTransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_55c3beb6-56f9-4d1e-8387-b255347b9e5f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_bbb71426-1d94-4a8e-8737-4b7d2a6c5cef" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_55c3beb6-56f9-4d1e-8387-b255347b9e5f" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_bbb71426-1d94-4a8e-8737-4b7d2a6c5cef" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramAxis_81b0f626-ca5e-4876-a59c-da81df099ef6" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ShareRepurchaseProgramAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_bbb71426-1d94-4a8e-8737-4b7d2a6c5cef" xlink:to="loc_srt_ShareRepurchaseProgramAxis_81b0f626-ca5e-4876-a59c-da81df099ef6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_81b0f626-ca5e-4876-a59c-da81df099ef6_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ShareRepurchaseProgramAxis_81b0f626-ca5e-4876-a59c-da81df099ef6" xlink:to="loc_srt_ShareRepurchaseProgramDomain_81b0f626-ca5e-4876-a59c-da81df099ef6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ShareRepurchaseProgramDomain_31174114-ac62-4cf4-8bb1-613f0abfde42" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ShareRepurchaseProgramDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ShareRepurchaseProgramAxis_81b0f626-ca5e-4876-a59c-da81df099ef6" xlink:to="loc_srt_ShareRepurchaseProgramDomain_31174114-ac62-4cf4-8bb1-613f0abfde42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_DistributionReinvestmentPlanMember_26615cc8-5f4e-4bc9-9764-0687b824b68e" xlink:href="fsk-20250331.xsd#fsk_DistributionReinvestmentPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ShareRepurchaseProgramDomain_31174114-ac62-4cf4-8bb1-613f0abfde42" xlink:to="loc_fsk_DistributionReinvestmentPlanMember_26615cc8-5f4e-4bc9-9764-0687b824b68e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_b03e27b1-c22b-4f6a-83c9-4b97d1f6161a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_bbb71426-1d94-4a8e-8737-4b7d2a6c5cef" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_b03e27b1-c22b-4f6a-83c9-4b97d1f6161a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_b03e27b1-c22b-4f6a-83c9-4b97d1f6161a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_b03e27b1-c22b-4f6a-83c9-4b97d1f6161a" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_b03e27b1-c22b-4f6a-83c9-4b97d1f6161a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_bc0b87eb-8f43-4551-bcbc-2bfd9710dcb4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_b03e27b1-c22b-4f6a-83c9-4b97d1f6161a" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_bc0b87eb-8f43-4551-bcbc-2bfd9710dcb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_05d26d1d-53d4-44ce-a673-79bc2536eece" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_bc0b87eb-8f43-4551-bcbc-2bfd9710dcb4" xlink:to="loc_us-gaap_SubsequentEventMember_05d26d1d-53d4-44ce-a673-79bc2536eece" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan_888dae28-1b5c-416c-af23-8f4279873664" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_55c3beb6-56f9-4d1e-8387-b255347b9e5f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesDividendReinvestmentPlan_888dae28-1b5c-416c-af23-8f4279873664" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_StockIssuedDuringPeriodDividendReinvestmentPlanAverageCostPerShare_a021d097-b086-4386-8f32-8f4b9db9efd7" xlink:href="fsk-20250331.xsd#fsk_StockIssuedDuringPeriodDividendReinvestmentPlanAverageCostPerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_55c3beb6-56f9-4d1e-8387-b255347b9e5f" xlink:to="loc_fsk_StockIssuedDuringPeriodDividendReinvestmentPlanAverageCostPerShare_a021d097-b086-4386-8f32-8f4b9db9efd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan_2e4cbf4b-30bf-4c19-8ccb-43c17796bbed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_55c3beb6-56f9-4d1e-8387-b255347b9e5f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueDividendReinvestmentPlan_2e4cbf4b-30bf-4c19-8ccb-43c17796bbed" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/RelatedPartyTransactionsNarrativeDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#RelatedPartyTransactionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/RelatedPartyTransactionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_0cb9482d-18eb-4376-a590-8e26c67231d7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_87800ee5-b1f2-47c7-811c-d83323429268" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_0cb9482d-18eb-4376-a590-8e26c67231d7" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_87800ee5-b1f2-47c7-811c-d83323429268" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_70f3371b-d9a5-419c-a0d4-b8e49cbc50a5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_87800ee5-b1f2-47c7-811c-d83323429268" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_70f3371b-d9a5-419c-a0d4-b8e49cbc50a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_70f3371b-d9a5-419c-a0d4-b8e49cbc50a5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_70f3371b-d9a5-419c-a0d4-b8e49cbc50a5" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_70f3371b-d9a5-419c-a0d4-b8e49cbc50a5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_ee00d098-1d57-4a76-9620-bf4a1b78d4f6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_70f3371b-d9a5-419c-a0d4-b8e49cbc50a5" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_ee00d098-1d57-4a76-9620-bf4a1b78d4f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentAdvisoryAgreementMember_3ba15813-8da4-49d4-8b20-09aa856dd1d0" xlink:href="fsk-20250331.xsd#fsk_InvestmentAdvisoryAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_ee00d098-1d57-4a76-9620-bf4a1b78d4f6" xlink:to="loc_fsk_InvestmentAdvisoryAgreementMember_3ba15813-8da4-49d4-8b20-09aa856dd1d0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AffiliatedPurchaserProgramMember_0195aa13-a6a1-498d-b037-d1488f96e54b" xlink:href="fsk-20250331.xsd#fsk_AffiliatedPurchaserProgramMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_ee00d098-1d57-4a76-9620-bf4a1b78d4f6" xlink:to="loc_fsk_AffiliatedPurchaserProgramMember_0195aa13-a6a1-498d-b037-d1488f96e54b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_ce2e6017-5e99-4c5f-9bab-5a8a2bb4c088" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_87800ee5-b1f2-47c7-811c-d83323429268" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_ce2e6017-5e99-4c5f-9bab-5a8a2bb4c088" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_ce2e6017-5e99-4c5f-9bab-5a8a2bb4c088_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_ce2e6017-5e99-4c5f-9bab-5a8a2bb4c088" xlink:to="loc_us-gaap_RelatedPartyDomain_ce2e6017-5e99-4c5f-9bab-5a8a2bb4c088_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_145b3be8-dccf-4408-9549-7cf46ff0c77c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_ce2e6017-5e99-4c5f-9bab-5a8a2bb4c088" xlink:to="loc_us-gaap_RelatedPartyDomain_145b3be8-dccf-4408-9549-7cf46ff0c77c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AffiliatedEntityMember_9f15d8ba-2119-4bcb-89d1-0815ca3c607f" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_AffiliatedEntityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_145b3be8-dccf-4408-9549-7cf46ff0c77c" xlink:to="loc_srt_AffiliatedEntityMember_9f15d8ba-2119-4bcb-89d1-0815ca3c607f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ManagementAndServiceFeesBaseRate_251924b0-ed60-4dda-bc8c-a1b6d15d85b0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ManagementAndServiceFeesBaseRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_0cb9482d-18eb-4376-a590-8e26c67231d7" xlink:to="loc_us-gaap_ManagementAndServiceFeesBaseRate_251924b0-ed60-4dda-bc8c-a1b6d15d85b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanySeniorSecurityIndebtednessAssetCoverageRatio_32996c49-b5b9-4aaa-bc17-ebc271183f78" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanySeniorSecurityIndebtednessAssetCoverageRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_0cb9482d-18eb-4376-a590-8e26c67231d7" xlink:to="loc_us-gaap_InvestmentCompanySeniorSecurityIndebtednessAssetCoverageRatio_32996c49-b5b9-4aaa-bc17-ebc271183f78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_RelatedPartyCommitmentToInvestmentVehicle_6732fd3f-f922-4f51-bd72-44b3df54557c" xlink:href="fsk-20250331.xsd#fsk_RelatedPartyCommitmentToInvestmentVehicle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_0cb9482d-18eb-4376-a590-8e26c67231d7" xlink:to="loc_fsk_RelatedPartyCommitmentToInvestmentVehicle_6732fd3f-f922-4f51-bd72-44b3df54557c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_RelatedPartyInvestmentVehicle_0d998f72-b9a6-4321-b1ea-bec419875547" xlink:href="fsk-20250331.xsd#fsk_RelatedPartyInvestmentVehicle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_0cb9482d-18eb-4376-a590-8e26c67231d7" xlink:to="loc_fsk_RelatedPartyInvestmentVehicle_0d998f72-b9a6-4321-b1ea-bec419875547" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/RelatedPartyTransactionsScheduleofFeesAndExpensesAccruedUnderTheInvestmentAdvisoryAgreementDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#RelatedPartyTransactionsScheduleofFeesAndExpensesAccruedUnderTheInvestmentAdvisoryAgreementDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/RelatedPartyTransactionsScheduleofFeesAndExpensesAccruedUnderTheInvestmentAdvisoryAgreementDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_43528f6a-644c-4a69-927b-b70bd6878fcb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_94b68947-a894-4921-9672-f0f58c1ecbd6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_43528f6a-644c-4a69-927b-b70bd6878fcb" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_94b68947-a894-4921-9672-f0f58c1ecbd6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_2e76a447-d0e0-48b6-86f0-5ec03294ae38" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_94b68947-a894-4921-9672-f0f58c1ecbd6" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_2e76a447-d0e0-48b6-86f0-5ec03294ae38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_2e76a447-d0e0-48b6-86f0-5ec03294ae38_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_2e76a447-d0e0-48b6-86f0-5ec03294ae38" xlink:to="loc_us-gaap_RelatedPartyDomain_2e76a447-d0e0-48b6-86f0-5ec03294ae38_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_42804e80-a1e8-4d66-b49f-71a8e8ca5824" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_2e76a447-d0e0-48b6-86f0-5ec03294ae38" xlink:to="loc_us-gaap_RelatedPartyDomain_42804e80-a1e8-4d66-b49f-71a8e8ca5824" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AffiliatedEntityMember_6ee28c81-435d-430e-82bf-064a1c0dbc1f" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_AffiliatedEntityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_42804e80-a1e8-4d66-b49f-71a8e8ca5824" xlink:to="loc_srt_AffiliatedEntityMember_6ee28c81-435d-430e-82bf-064a1c0dbc1f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ManagementFeeExpense_8d9706cb-e8f0-4207-a93d-1d24d46817c4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ManagementFeeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_43528f6a-644c-4a69-927b-b70bd6878fcb" xlink:to="loc_us-gaap_ManagementFeeExpense_8d9706cb-e8f0-4207-a93d-1d24d46817c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncentiveFeeExpense_6c9f027c-e832-4508-9f79-69a5d16d644e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncentiveFeeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_43528f6a-644c-4a69-927b-b70bd6878fcb" xlink:to="loc_us-gaap_IncentiveFeeExpense_6c9f027c-e832-4508-9f79-69a5d16d644e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdministrativeFeesExpense_2311d5eb-cea6-45aa-909f-ca6175075425" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AdministrativeFeesExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_43528f6a-644c-4a69-927b-b70bd6878fcb" xlink:to="loc_us-gaap_AdministrativeFeesExpense_2311d5eb-cea6-45aa-909f-ca6175075425" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentForManagementFee_1b966495-353a-4a43-8771-563f3b5a79fa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentForManagementFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_43528f6a-644c-4a69-927b-b70bd6878fcb" xlink:to="loc_us-gaap_PaymentForManagementFee_1b966495-353a-4a43-8771-563f3b5a79fa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ManagementFeePayable_79e946ff-ce37-40a6-af27-8783b97b15ce" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ManagementFeePayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_43528f6a-644c-4a69-927b-b70bd6878fcb" xlink:to="loc_us-gaap_ManagementFeePayable_79e946ff-ce37-40a6-af27-8783b97b15ce" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentForIncentiveFee_7db8b294-ede1-480f-ac41-2a4b68007f5d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentForIncentiveFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_43528f6a-644c-4a69-927b-b70bd6878fcb" xlink:to="loc_us-gaap_PaymentForIncentiveFee_7db8b294-ede1-480f-ac41-2a4b68007f5d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncentiveFeePayable_bb2e5d5b-ca97-428f-8a2d-d4bf417fda44" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncentiveFeePayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_43528f6a-644c-4a69-927b-b70bd6878fcb" xlink:to="loc_us-gaap_IncentiveFeePayable_bb2e5d5b-ca97-428f-8a2d-d4bf417fda44" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AdministrativeFeeExpenseAllocationOfAdministrativeCost_0494714e-ea48-4aa7-ae26-379dfe62b52f" xlink:href="fsk-20250331.xsd#fsk_AdministrativeFeeExpenseAllocationOfAdministrativeCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_43528f6a-644c-4a69-927b-b70bd6878fcb" xlink:to="loc_fsk_AdministrativeFeeExpenseAllocationOfAdministrativeCost_0494714e-ea48-4aa7-ae26-379dfe62b52f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AdministrativeFeeExpenseBrokenDealCost_35383d90-cbdf-4f91-a08d-aca7cd10f6f3" xlink:href="fsk-20250331.xsd#fsk_AdministrativeFeeExpenseBrokenDealCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_43528f6a-644c-4a69-927b-b70bd6878fcb" xlink:to="loc_fsk_AdministrativeFeeExpenseBrokenDealCost_35383d90-cbdf-4f91-a08d-aca7cd10f6f3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentForAdministrativeFees_c0ae60ac-f926-416d-9d35-f09849340bbd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_PaymentForAdministrativeFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_43528f6a-644c-4a69-927b-b70bd6878fcb" xlink:to="loc_us-gaap_PaymentForAdministrativeFees_c0ae60ac-f926-416d-9d35-f09849340bbd" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/DistributionsScheduleofCashDistributionsDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#DistributionsScheduleofCashDistributionsDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/DistributionsScheduleofCashDistributionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ScheduleOfDistributionLineItems_7f442abc-7bf9-49f1-9c74-aee13caf5a5c" xlink:href="fsk-20250331.xsd#fsk_ScheduleOfDistributionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ScheduleOfDistributionTable_344b5a3d-6ce1-4dd1-a46e-358bd26d204e" xlink:href="fsk-20250331.xsd#fsk_ScheduleOfDistributionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_7f442abc-7bf9-49f1-9c74-aee13caf5a5c" xlink:to="loc_fsk_ScheduleOfDistributionTable_344b5a3d-6ce1-4dd1-a46e-358bd26d204e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsAxis_1201fa3e-ca99-49c1-b883-fe0665dc76ad" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_fsk_ScheduleOfDistributionTable_344b5a3d-6ce1-4dd1-a46e-358bd26d204e" xlink:to="loc_us-gaap_DividendsAxis_1201fa3e-ca99-49c1-b883-fe0665dc76ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_1201fa3e-ca99-49c1-b883-fe0665dc76ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DividendsAxis_1201fa3e-ca99-49c1-b883-fe0665dc76ad" xlink:to="loc_us-gaap_DividendsDomain_1201fa3e-ca99-49c1-b883-fe0665dc76ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_05bdcdf9-5e5c-4a6e-8c86-5a89216aa8e0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DividendsAxis_1201fa3e-ca99-49c1-b883-fe0665dc76ad" xlink:to="loc_us-gaap_DividendsDomain_05bdcdf9-5e5c-4a6e-8c86-5a89216aa8e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_O2025M2AggregateDividendsMember_a144686e-b662-4221-b41b-ae5988d69ec6" xlink:href="fsk-20250331.xsd#fsk_O2025M2AggregateDividendsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DividendsDomain_05bdcdf9-5e5c-4a6e-8c86-5a89216aa8e0" xlink:to="loc_fsk_O2025M2AggregateDividendsMember_a144686e-b662-4221-b41b-ae5988d69ec6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_S2023M11DividendsMember_f74ba6a7-d7f5-466a-8d3b-2b5cf7baef5d" xlink:href="fsk-20250331.xsd#fsk_S2023M11DividendsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DividendsDomain_05bdcdf9-5e5c-4a6e-8c86-5a89216aa8e0" xlink:to="loc_fsk_S2023M11DividendsMember_f74ba6a7-d7f5-466a-8d3b-2b5cf7baef5d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_O2024M2AggregateDividendsMember_866135a1-b8fc-4c08-8d47-b23626fabc9a" xlink:href="fsk-20250331.xsd#fsk_O2024M2AggregateDividendsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DividendsDomain_05bdcdf9-5e5c-4a6e-8c86-5a89216aa8e0" xlink:to="loc_fsk_O2024M2AggregateDividendsMember_866135a1-b8fc-4c08-8d47-b23626fabc9a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CommonStockDividendsPerShareDeclaredOrdinary_8e6ca329-dc5d-46ac-bcdc-7de4d5dbdd35" xlink:href="fsk-20250331.xsd#fsk_CommonStockDividendsPerShareDeclaredOrdinary"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_7f442abc-7bf9-49f1-9c74-aee13caf5a5c" xlink:to="loc_fsk_CommonStockDividendsPerShareDeclaredOrdinary_8e6ca329-dc5d-46ac-bcdc-7de4d5dbdd35" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CommonStockDividendsPerShareDeclaredSupplemental_322323ef-7e5e-4e17-a8ab-7cff77add494" xlink:href="fsk-20250331.xsd#fsk_CommonStockDividendsPerShareDeclaredSupplemental"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_7f442abc-7bf9-49f1-9c74-aee13caf5a5c" xlink:to="loc_fsk_CommonStockDividendsPerShareDeclaredSupplemental_322323ef-7e5e-4e17-a8ab-7cff77add494" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CommonStockDividendsPerShareDeclaredSpecial_6b52a87b-0573-45cd-be55-1c234d203f84" xlink:href="fsk-20250331.xsd#fsk_CommonStockDividendsPerShareDeclaredSpecial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_7f442abc-7bf9-49f1-9c74-aee13caf5a5c" xlink:to="loc_fsk_CommonStockDividendsPerShareDeclaredSpecial_6b52a87b-0573-45cd-be55-1c234d203f84" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_67cea8db-e7fc-4b01-a4c3-e3d96def1f3f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_7f442abc-7bf9-49f1-9c74-aee13caf5a5c" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_67cea8db-e7fc-4b01-a4c3-e3d96def1f3f" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/DistributionsNarrativeDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#DistributionsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/DistributionsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ScheduleOfDistributionLineItems_72b7fbe5-a6e9-43a6-8109-85defe1ca451" xlink:href="fsk-20250331.xsd#fsk_ScheduleOfDistributionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ScheduleOfDistributionTable_aad56986-3f3b-4dcc-801d-ae0f43df6131" xlink:href="fsk-20250331.xsd#fsk_ScheduleOfDistributionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_72b7fbe5-a6e9-43a6-8109-85defe1ca451" xlink:to="loc_fsk_ScheduleOfDistributionTable_aad56986-3f3b-4dcc-801d-ae0f43df6131" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_dfad4772-c840-4395-b6b6-d4aec9309353" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_fsk_ScheduleOfDistributionTable_aad56986-3f3b-4dcc-801d-ae0f43df6131" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_dfad4772-c840-4395-b6b6-d4aec9309353" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_dfad4772-c840-4395-b6b6-d4aec9309353_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_dfad4772-c840-4395-b6b6-d4aec9309353" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_dfad4772-c840-4395-b6b6-d4aec9309353_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_42f1f5b8-f164-4916-b6b9-b78be3e3ddce" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_dfad4772-c840-4395-b6b6-d4aec9309353" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_42f1f5b8-f164-4916-b6b9-b78be3e3ddce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_897739dd-1faa-4a9a-931c-60b64bda8541" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_42f1f5b8-f164-4916-b6b9-b78be3e3ddce" xlink:to="loc_us-gaap_SubsequentEventMember_897739dd-1faa-4a9a-931c-60b64bda8541" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_b2a01d57-a6f9-4f08-944a-88c8d8ff56cb" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_fsk_ScheduleOfDistributionTable_aad56986-3f3b-4dcc-801d-ae0f43df6131" xlink:to="loc_srt_ConsolidatedEntitiesAxis_b2a01d57-a6f9-4f08-944a-88c8d8ff56cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_b2a01d57-a6f9-4f08-944a-88c8d8ff56cb_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_b2a01d57-a6f9-4f08-944a-88c8d8ff56cb" xlink:to="loc_srt_ConsolidatedEntitiesDomain_b2a01d57-a6f9-4f08-944a-88c8d8ff56cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_0738b7f5-1a85-4f99-9673-ebdf1c222813" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_b2a01d57-a6f9-4f08-944a-88c8d8ff56cb" xlink:to="loc_srt_ConsolidatedEntitiesDomain_0738b7f5-1a85-4f99-9673-ebdf1c222813" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_b8f6bf41-d0f0-4878-bed5-8356776d0906" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_0738b7f5-1a85-4f99-9673-ebdf1c222813" xlink:to="loc_srt_SubsidiariesMember_b8f6bf41-d0f0-4878-bed5-8356776d0906" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsAxis_8f75feea-4577-4342-8f70-caed2daef517" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_fsk_ScheduleOfDistributionTable_aad56986-3f3b-4dcc-801d-ae0f43df6131" xlink:to="loc_us-gaap_DividendsAxis_8f75feea-4577-4342-8f70-caed2daef517" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_8f75feea-4577-4342-8f70-caed2daef517_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DividendsAxis_8f75feea-4577-4342-8f70-caed2daef517" xlink:to="loc_us-gaap_DividendsDomain_8f75feea-4577-4342-8f70-caed2daef517_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_008bd283-0c13-4e31-b90b-9d8f19c76cfa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DividendsAxis_8f75feea-4577-4342-8f70-caed2daef517" xlink:to="loc_us-gaap_DividendsDomain_008bd283-0c13-4e31-b90b-9d8f19c76cfa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_O2025Q2RegularDividendsMember_94ce67d9-8815-41d2-acdf-dbb3a76d31b0" xlink:href="fsk-20250331.xsd#fsk_O2025Q2RegularDividendsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DividendsDomain_008bd283-0c13-4e31-b90b-9d8f19c76cfa" xlink:to="loc_fsk_O2025Q2RegularDividendsMember_94ce67d9-8815-41d2-acdf-dbb3a76d31b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_O2025Q2SupplementalDividendsMember_2a7cbb7f-439b-4c0a-a386-8cce23f2bf0b" xlink:href="fsk-20250331.xsd#fsk_O2025Q2SupplementalDividendsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DividendsDomain_008bd283-0c13-4e31-b90b-9d8f19c76cfa" xlink:to="loc_fsk_O2025Q2SupplementalDividendsMember_2a7cbb7f-439b-4c0a-a386-8cce23f2bf0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_457d9e31-f6b9-4ac0-a154-cf56f8f554fe" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_72b7fbe5-a6e9-43a6-8109-85defe1ca451" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_457d9e31-f6b9-4ac0-a154-cf56f8f554fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_StockIssuedDuringPeriodDividendReinvestmentPlanPercentOfMarketPrice_eea9d948-16ec-4f56-87e5-a4fff8a97314" xlink:href="fsk-20250331.xsd#fsk_StockIssuedDuringPeriodDividendReinvestmentPlanPercentOfMarketPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_72b7fbe5-a6e9-43a6-8109-85defe1ca451" xlink:to="loc_fsk_StockIssuedDuringPeriodDividendReinvestmentPlanPercentOfMarketPrice_eea9d948-16ec-4f56-87e5-a4fff8a97314" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyDistributableEarningsLossAccumulatedCapitalLossCarryforward_838a6c80-9331-47b7-9282-d94053fe4885" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyDistributableEarningsLossAccumulatedCapitalLossCarryforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_72b7fbe5-a6e9-43a6-8109-85defe1ca451" xlink:to="loc_us-gaap_InvestmentCompanyDistributableEarningsLossAccumulatedCapitalLossCarryforward_838a6c80-9331-47b7-9282-d94053fe4885" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxBasisOfInvestmentsGrossUnrealizedAppreciation_92a1e11a-8959-44b1-a33a-cd1050b03113" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TaxBasisOfInvestmentsGrossUnrealizedAppreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_72b7fbe5-a6e9-43a6-8109-85defe1ca451" xlink:to="loc_us-gaap_TaxBasisOfInvestmentsGrossUnrealizedAppreciation_92a1e11a-8959-44b1-a33a-cd1050b03113" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxBasisOfInvestmentsGrossUnrealizedDepreciation_c341dfc6-15ef-4b51-acc2-d797f62fd5ca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TaxBasisOfInvestmentsGrossUnrealizedDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_72b7fbe5-a6e9-43a6-8109-85defe1ca451" xlink:to="loc_us-gaap_TaxBasisOfInvestmentsGrossUnrealizedDepreciation_c341dfc6-15ef-4b51-acc2-d797f62fd5ca" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxBasisOfInvestmentsCostForIncomeTaxPurposes_e5d4280d-e023-4c21-b1d9-1bddaa4957b5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TaxBasisOfInvestmentsCostForIncomeTaxPurposes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_72b7fbe5-a6e9-43a6-8109-85defe1ca451" xlink:to="loc_us-gaap_TaxBasisOfInvestmentsCostForIncomeTaxPurposes_e5d4280d-e023-4c21-b1d9-1bddaa4957b5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxBasisOfInvestmentsUnrealizedAppreciationDepreciationNet_5612646c-2bb2-4350-ad0e-2bd81514541f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TaxBasisOfInvestmentsUnrealizedAppreciationDepreciationNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_72b7fbe5-a6e9-43a6-8109-85defe1ca451" xlink:to="loc_us-gaap_TaxBasisOfInvestmentsUnrealizedAppreciationDepreciationNet_5612646c-2bb2-4350-ad0e-2bd81514541f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesInvestments_b5e6ab8d-33ce-4c2b-b382-3894104d4736" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredTaxLiabilitiesInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_72b7fbe5-a6e9-43a6-8109-85defe1ca451" xlink:to="loc_us-gaap_DeferredTaxLiabilitiesInvestments_b5e6ab8d-33ce-4c2b-b382-3894104d4736" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsInvestments_47bcb328-ce57-4afb-8706-f809cc635534" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredTaxAssetsInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_72b7fbe5-a6e9-43a6-8109-85defe1ca451" xlink:to="loc_us-gaap_DeferredTaxAssetsInvestments_47bcb328-ce57-4afb-8706-f809cc635534" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsValuationAllowance_03f378a6-a5f3-464f-aa6c-63d2db19a64c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DeferredTaxAssetsValuationAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_fsk_ScheduleOfDistributionLineItems_72b7fbe5-a6e9-43a6-8109-85defe1ca451" xlink:to="loc_us-gaap_DeferredTaxAssetsValuationAllowance_03f378a6-a5f3-464f-aa6c-63d2db19a64c" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/InvestmentPortfolioScheduleofInvestmentPortfolioAtCostAndFairValueDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#InvestmentPortfolioScheduleofInvestmentPortfolioAtCostAndFairValueDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/InvestmentPortfolioScheduleofInvestmentPortfolioAtCostAndFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsLineItems_5511fb7c-a6bc-4282-bba1-e0a7c119db23" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsTable_f00c8881-abe9-40b5-ae8d-cc7128aa50a4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_5511fb7c-a6bc-4282-bba1-e0a7c119db23" xlink:to="loc_us-gaap_ScheduleOfInvestmentsTable_f00c8881-abe9-40b5-ae8d-cc7128aa50a4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_1d6aa4bb-e66f-4e0a-9a7a-3cc0f10eeca1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_f00c8881-abe9-40b5-ae8d-cc7128aa50a4" xlink:to="loc_us-gaap_InvestmentTypeAxis_1d6aa4bb-e66f-4e0a-9a7a-3cc0f10eeca1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_1d6aa4bb-e66f-4e0a-9a7a-3cc0f10eeca1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_1d6aa4bb-e66f-4e0a-9a7a-3cc0f10eeca1" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_1d6aa4bb-e66f-4e0a-9a7a-3cc0f10eeca1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_f621b10d-c00a-4f12-a6a5-ac4359cad1b2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_1d6aa4bb-e66f-4e0a-9a7a-3cc0f10eeca1" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_f621b10d-c00a-4f12-a6a5-ac4359cad1b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SeniorSecuredLoansFirstLienMember_fab8b5f6-e302-4423-b94e-c8e98ef1e488" xlink:href="fsk-20250331.xsd#fsk_SeniorSecuredLoansFirstLienMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_f621b10d-c00a-4f12-a6a5-ac4359cad1b2" xlink:to="loc_fsk_SeniorSecuredLoansFirstLienMember_fab8b5f6-e302-4423-b94e-c8e98ef1e488" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SeniorSecuredLoansSecondLienMember_4ebb0f33-880a-4e2f-888b-e1383b9fdcbd" xlink:href="fsk-20250331.xsd#fsk_SeniorSecuredLoansSecondLienMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_f621b10d-c00a-4f12-a6a5-ac4359cad1b2" xlink:to="loc_fsk_SeniorSecuredLoansSecondLienMember_4ebb0f33-880a-4e2f-888b-e1383b9fdcbd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_DebtSecuritiesOtherSeniorSecuredDebtMember_abef2000-55d2-4284-92bd-24e142f0f185" xlink:href="fsk-20250331.xsd#fsk_DebtSecuritiesOtherSeniorSecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_f621b10d-c00a-4f12-a6a5-ac4359cad1b2" xlink:to="loc_fsk_DebtSecuritiesOtherSeniorSecuredDebtMember_abef2000-55d2-4284-92bd-24e142f0f185" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedDebtMember_6bdeb2aa-8737-437b-a06e-ed654f4819d8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubordinatedDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_f621b10d-c00a-4f12-a6a5-ac4359cad1b2" xlink:to="loc_us-gaap_SubordinatedDebtMember_6bdeb2aa-8737-437b-a06e-ed654f4819d8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AssetBasedFinanceMember_da4cdff6-6b58-4307-874d-8a3cee10b882" xlink:href="fsk-20250331.xsd#fsk_AssetBasedFinanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_f621b10d-c00a-4f12-a6a5-ac4359cad1b2" xlink:to="loc_fsk_AssetBasedFinanceMember_da4cdff6-6b58-4307-874d-8a3cee10b882" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_f5c26031-6c31-4b81-b792-74effdb85519" xlink:href="fsk-20250331.xsd#fsk_CreditOpportunitiesPartnersJVLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_f621b10d-c00a-4f12-a6a5-ac4359cad1b2" xlink:to="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_f5c26031-6c31-4b81-b792-74effdb85519" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_EquityOtherMember_2d5dcc8d-c182-4102-86f8-c6d1801802b3" xlink:href="fsk-20250331.xsd#fsk_EquityOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_f621b10d-c00a-4f12-a6a5-ac4359cad1b2" xlink:to="loc_fsk_EquityOtherMember_2d5dcc8d-c182-4102-86f8-c6d1801802b3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_578326f2-67c7-4aa0-a5e7-e0f4cb1e039c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_f00c8881-abe9-40b5-ae8d-cc7128aa50a4" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_578326f2-67c7-4aa0-a5e7-e0f4cb1e039c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_578326f2-67c7-4aa0-a5e7-e0f4cb1e039c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_578326f2-67c7-4aa0-a5e7-e0f4cb1e039c" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_578326f2-67c7-4aa0-a5e7-e0f4cb1e039c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_e0bfa4d1-3cf7-4804-a138-09d8b81a5408" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_578326f2-67c7-4aa0-a5e7-e0f4cb1e039c" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_e0bfa4d1-3cf7-4804-a138-09d8b81a5408" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentOwnedAtFairValueMember_d53fbe49-1659-4994-9779-e38707134a74" xlink:href="fsk-20250331.xsd#fsk_InvestmentOwnedAtFairValueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_e0bfa4d1-3cf7-4804-a138-09d8b81a5408" xlink:to="loc_fsk_InvestmentOwnedAtFairValueMember_d53fbe49-1659-4994-9779-e38707134a74" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_d4586a6e-ab33-4061-b2db-2282e0ecda4a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_f00c8881-abe9-40b5-ae8d-cc7128aa50a4" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_d4586a6e-ab33-4061-b2db-2282e0ecda4a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_d4586a6e-ab33-4061-b2db-2282e0ecda4a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_d4586a6e-ab33-4061-b2db-2282e0ecda4a" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_d4586a6e-ab33-4061-b2db-2282e0ecda4a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_ca278c23-0e0f-4e7e-a281-a20fb7dce32f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_d4586a6e-ab33-4061-b2db-2282e0ecda4a" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_ca278c23-0e0f-4e7e-a281-a20fb7dce32f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_eedfc520-d309-4521-855f-130107e95151" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_ca278c23-0e0f-4e7e-a281-a20fb7dce32f" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_eedfc520-d309-4521-855f-130107e95151" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtCost_236ccd69-2006-429e-965b-abb0c5f914b5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_5511fb7c-a6bc-4282-bba1-e0a7c119db23" xlink:to="loc_us-gaap_InvestmentOwnedAtCost_236ccd69-2006-429e-965b-abb0c5f914b5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtFairValue_d964e6ed-819a-486b-90c1-38d529438880" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_5511fb7c-a6bc-4282-bba1-e0a7c119db23" xlink:to="loc_us-gaap_InvestmentOwnedAtFairValue_d964e6ed-819a-486b-90c1-38d529438880" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_17e20643-a016-4bc7-9e62-2b75d6a3e98f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_5511fb7c-a6bc-4282-bba1-e0a7c119db23" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_17e20643-a016-4bc7-9e62-2b75d6a3e98f" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/InvestmentPortfolioNarrativeDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#InvestmentPortfolioNarrativeDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/InvestmentPortfolioNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsLineItems_2491dd3f-9936-4b06-adc1-170ea1f5385f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfInvestmentsTable_0c905c7b-5888-468d-b92c-b69d9ed72c91" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_2491dd3f-9936-4b06-adc1-170ea1f5385f" xlink:to="loc_us-gaap_ScheduleOfInvestmentsTable_0c905c7b-5888-468d-b92c-b69d9ed72c91" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationAxis_f91cfd20-d69e-47a0-8a4c-20c8a74942c8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_0c905c7b-5888-468d-b92c-b69d9ed72c91" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationAxis_f91cfd20-d69e-47a0-8a4c-20c8a74942c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationDomain_f91cfd20-d69e-47a0-8a4c-20c8a74942c8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationAxis_f91cfd20-d69e-47a0-8a4c-20c8a74942c8" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationDomain_f91cfd20-d69e-47a0-8a4c-20c8a74942c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIssuerAffiliationDomain_1b85cdb3-23c2-490a-ac71-dd9e7568a66c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIssuerAffiliationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationAxis_f91cfd20-d69e-47a0-8a4c-20c8a74942c8" xlink:to="loc_us-gaap_InvestmentIssuerAffiliationDomain_1b85cdb3-23c2-490a-ac71-dd9e7568a66c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentAffiliatedIssuerControlledMember_9a8791d9-04f4-4da4-881b-c65914d40701" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentAffiliatedIssuerControlledMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_1b85cdb3-23c2-490a-ac71-dd9e7568a66c" xlink:to="loc_us-gaap_InvestmentAffiliatedIssuerControlledMember_9a8791d9-04f4-4da4-881b-c65914d40701" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember_395a6849-d48d-49cd-9e83-f9dbd069d68e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentIssuerAffiliationDomain_1b85cdb3-23c2-490a-ac71-dd9e7568a66c" xlink:to="loc_us-gaap_InvestmentAffiliatedIssuerNoncontrolledMember_395a6849-d48d-49cd-9e83-f9dbd069d68e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_3e9d8850-3106-4d6a-a6c3-7fc622ac2a3f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_0c905c7b-5888-468d-b92c-b69d9ed72c91" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_3e9d8850-3106-4d6a-a6c3-7fc622ac2a3f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_3e9d8850-3106-4d6a-a6c3-7fc622ac2a3f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_3e9d8850-3106-4d6a-a6c3-7fc622ac2a3f" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_3e9d8850-3106-4d6a-a6c3-7fc622ac2a3f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_d8b49818-f87e-4065-ac17-9daaab54723e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_3e9d8850-3106-4d6a-a6c3-7fc622ac2a3f" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_d8b49818-f87e-4065-ac17-9daaab54723e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_UnfundedDebtSecuritiesMember_cef40487-55f5-4525-97dc-345c0e199e04" xlink:href="fsk-20250331.xsd#fsk_UnfundedDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_d8b49818-f87e-4065-ac17-9daaab54723e" xlink:to="loc_fsk_UnfundedDebtSecuritiesMember_cef40487-55f5-4525-97dc-345c0e199e04" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_UnfundedEquityOtherCommitmentsMember_37ed0123-5a23-4b55-9876-3d71e54a455d" xlink:href="fsk-20250331.xsd#fsk_UnfundedEquityOtherCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_d8b49818-f87e-4065-ac17-9daaab54723e" xlink:to="loc_fsk_UnfundedEquityOtherCommitmentsMember_37ed0123-5a23-4b55-9876-3d71e54a455d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_PartnershipInterestMember_36656244-229c-4835-9649-533870d12eae" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_PartnershipInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_d8b49818-f87e-4065-ac17-9daaab54723e" xlink:to="loc_srt_PartnershipInterestMember_36656244-229c-4835-9649-533870d12eae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis_480ffd64-3977-4eef-8573-09da8e593f87" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfInvestmentsTable_0c905c7b-5888-468d-b92c-b69d9ed72c91" xlink:to="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis_480ffd64-3977-4eef-8573-09da8e593f87" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_480ffd64-3977-4eef-8573-09da8e593f87_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis_480ffd64-3977-4eef-8573-09da8e593f87" xlink:to="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_480ffd64-3977-4eef-8573-09da8e593f87_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_3ad1b5bc-10ec-44cc-a526-9c31fb241106" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis_480ffd64-3977-4eef-8573-09da8e593f87" xlink:to="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_3ad1b5bc-10ec-44cc-a526-9c31fb241106" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_2be68b45-4d17-499b-a096-9e659be7b8cf" xlink:href="fsk-20250331.xsd#fsk_CreditOpportunitiesPartnersJVLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_3ad1b5bc-10ec-44cc-a526-9c31fb241106" xlink:to="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_2be68b45-4d17-499b-a096-9e659be7b8cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_FSKKRCapitalCorpMember_9155893c-2817-4e6b-b1c6-67f844270d61" xlink:href="fsk-20250331.xsd#fsk_FSKKRCapitalCorpMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_3ad1b5bc-10ec-44cc-a526-9c31fb241106" xlink:to="loc_fsk_FSKKRCapitalCorpMember_9155893c-2817-4e6b-b1c6-67f844270d61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SouthCarolinaRetirementSystemsGroupTrustMember_525adb3e-d56a-45e0-bf49-5e9875f32073" xlink:href="fsk-20250331.xsd#fsk_SouthCarolinaRetirementSystemsGroupTrustMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_3ad1b5bc-10ec-44cc-a526-9c31fb241106" xlink:to="loc_fsk_SouthCarolinaRetirementSystemsGroupTrustMember_525adb3e-d56a-45e0-bf49-5e9875f32073" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_NumberOfInvestmentsInPortfolioCompanies_44b3c976-4029-4aac-9edf-08ce3375a7b8" xlink:href="fsk-20250331.xsd#fsk_NumberOfInvestmentsInPortfolioCompanies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_2491dd3f-9936-4b06-adc1-170ea1f5385f" xlink:to="loc_fsk_NumberOfInvestmentsInPortfolioCompanies_44b3c976-4029-4aac-9edf-08ce3375a7b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyFinancialCommitmentToInvesteeFutureAmount_cbfd336d-f1fc-48da-82d0-71c8b957ae4c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyFinancialCommitmentToInvesteeFutureAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_2491dd3f-9936-4b06-adc1-170ea1f5385f" xlink:to="loc_us-gaap_InvestmentCompanyFinancialCommitmentToInvesteeFutureAmount_cbfd336d-f1fc-48da-82d0-71c8b957ae4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyCommittedCapital_e42777d2-7ff1-44f6-8d11-50b9cf0ab930" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyCommittedCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_2491dd3f-9936-4b06-adc1-170ea1f5385f" xlink:to="loc_us-gaap_InvestmentCompanyCommittedCapital_e42777d2-7ff1-44f6-8d11-50b9cf0ab930" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyContributedCapitalToCommittedCapitalRatio_385ed025-e30b-4e12-916f-f89169f88769" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyContributedCapitalToCommittedCapitalRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_2491dd3f-9936-4b06-adc1-170ea1f5385f" xlink:to="loc_us-gaap_InvestmentCompanyContributedCapitalToCommittedCapitalRatio_385ed025-e30b-4e12-916f-f89169f88769" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentCompanyCommittedCapitalVotingControlPercentage_377da3a7-5003-4279-bcf9-58b6ecd070f4" xlink:href="fsk-20250331.xsd#fsk_InvestmentCompanyCommittedCapitalVotingControlPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_2491dd3f-9936-4b06-adc1-170ea1f5385f" xlink:to="loc_fsk_InvestmentCompanyCommittedCapitalVotingControlPercentage_377da3a7-5003-4279-bcf9-58b6ecd070f4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentCompanyCommittedCapitalFundedToJointVenture_71a8d4ec-8f16-408d-98cd-02c91a338473" xlink:href="fsk-20250331.xsd#fsk_InvestmentCompanyCommittedCapitalFundedToJointVenture"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_2491dd3f-9936-4b06-adc1-170ea1f5385f" xlink:to="loc_fsk_InvestmentCompanyCommittedCapitalFundedToJointVenture_71a8d4ec-8f16-408d-98cd-02c91a338473" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_DebtAndEquitySecuritiesSoldCostBasis_230b050a-3c1a-4e2c-94d7-2d2ca9e3d044" xlink:href="fsk-20250331.xsd#fsk_DebtAndEquitySecuritiesSoldCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_2491dd3f-9936-4b06-adc1-170ea1f5385f" xlink:to="loc_fsk_DebtAndEquitySecuritiesSoldCostBasis_230b050a-3c1a-4e2c-94d7-2d2ca9e3d044" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfEquitySecuritiesFvNi_0e0ee367-f7eb-46c4-a518-4ddac9fc0c15" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProceedsFromSaleOfEquitySecuritiesFvNi"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_2491dd3f-9936-4b06-adc1-170ea1f5385f" xlink:to="loc_us-gaap_ProceedsFromSaleOfEquitySecuritiesFvNi_0e0ee367-f7eb-46c4-a518-4ddac9fc0c15" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtAndEquitySecuritiesRealizedGainLoss_ec57ec11-87ea-4637-959f-be47428e95fc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtAndEquitySecuritiesRealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_2491dd3f-9936-4b06-adc1-170ea1f5385f" xlink:to="loc_us-gaap_DebtAndEquitySecuritiesRealizedGainLoss_ec57ec11-87ea-4637-959f-be47428e95fc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableInvestmentSale_f1dfb1da-1e3b-479f-81d6-dd4b30e908bf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ReceivableInvestmentSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_2491dd3f-9936-4b06-adc1-170ea1f5385f" xlink:to="loc_us-gaap_ReceivableInvestmentSale_f1dfb1da-1e3b-479f-81d6-dd4b30e908bf" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentCompanyCommittedCapitalPercentageOfFeeEntitledOnAssetsUnderAdministration_e0e30fcb-d37c-402d-a5db-dd3e90f68678" xlink:href="fsk-20250331.xsd#fsk_InvestmentCompanyCommittedCapitalPercentageOfFeeEntitledOnAssetsUnderAdministration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_2491dd3f-9936-4b06-adc1-170ea1f5385f" xlink:to="loc_fsk_InvestmentCompanyCommittedCapitalPercentageOfFeeEntitledOnAssetsUnderAdministration_e0e30fcb-d37c-402d-a5db-dd3e90f68678" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AdministrativeServicesExpenses_125d0cf7-afe8-48a1-9e45-b7c8604d864c" xlink:href="fsk-20250331.xsd#fsk_AdministrativeServicesExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfInvestmentsLineItems_2491dd3f-9936-4b06-adc1-170ea1f5385f" xlink:to="loc_fsk_AdministrativeServicesExpenses_125d0cf7-afe8-48a1-9e45-b7c8604d864c" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/InvestmentPortfolioScheduleofInvestmentPortfolioatFairValueandPercentageDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#InvestmentPortfolioScheduleofInvestmentPortfolioatFairValueandPercentageDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/InvestmentPortfolioScheduleofInvestmentPortfolioatFairValueandPercentageDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_ab08a2f3-c3e6-41dd-9561-709300f8e2a5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryTable_3ef4d989-c079-4982-9494-06d97ac229bc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_ab08a2f3-c3e6-41dd-9561-709300f8e2a5" xlink:to="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryTable_3ef4d989-c079-4982-9494-06d97ac229bc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesByIndustryAxis_6576936c-3e27-46d4-9e14-51dc4f3c3d71" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesByIndustryAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryTable_3ef4d989-c079-4982-9494-06d97ac229bc" xlink:to="loc_us-gaap_EquitySecuritiesByIndustryAxis_6576936c-3e27-46d4-9e14-51dc4f3c3d71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesIndustryMember_6576936c-3e27-46d4-9e14-51dc4f3c3d71_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesIndustryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_EquitySecuritiesByIndustryAxis_6576936c-3e27-46d4-9e14-51dc4f3c3d71" xlink:to="loc_us-gaap_EquitySecuritiesIndustryMember_6576936c-3e27-46d4-9e14-51dc4f3c3d71_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EquitySecuritiesIndustryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_EquitySecuritiesByIndustryAxis_6576936c-3e27-46d4-9e14-51dc4f3c3d71" xlink:to="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AutomobilesComponentsSectorMember_5d48f9f4-39fc-4b6e-a989-955115e0cb60" xlink:href="fsk-20250331.xsd#fsk_AutomobilesComponentsSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_AutomobilesComponentsSectorMember_5d48f9f4-39fc-4b6e-a989-955115e0cb60" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_BanksSectorMember_75a70a3f-eff0-42c0-b098-6ed08cadb653" xlink:href="fsk-20250331.xsd#fsk_BanksSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_BanksSectorMember_75a70a3f-eff0-42c0-b098-6ed08cadb653" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CapitalGoodsSectorMember_62945729-eedf-498b-a6fd-1bda1044e1aa" xlink:href="fsk-20250331.xsd#fsk_CapitalGoodsSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_CapitalGoodsSectorMember_62945729-eedf-498b-a6fd-1bda1044e1aa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CommercialAndProfessionalServicesSectorMember_cf76bb04-8d81-4d2b-b68a-63bc195734e2" xlink:href="fsk-20250331.xsd#fsk_CommercialAndProfessionalServicesSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_CommercialAndProfessionalServicesSectorMember_cf76bb04-8d81-4d2b-b68a-63bc195734e2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ConsumerDiscretionaryDistributionRetailSectorMember_edf79b51-615c-4b2d-8210-fbc3dc994f35" xlink:href="fsk-20250331.xsd#fsk_ConsumerDiscretionaryDistributionRetailSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_ConsumerDiscretionaryDistributionRetailSectorMember_edf79b51-615c-4b2d-8210-fbc3dc994f35" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ConsumerDurablesApparelSectorMember_4167b97f-d64b-4081-a8e6-3f2fefbde44f" xlink:href="fsk-20250331.xsd#fsk_ConsumerDurablesApparelSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_ConsumerDurablesApparelSectorMember_4167b97f-d64b-4081-a8e6-3f2fefbde44f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ConsumerServicesSectorMember_4997448b-4160-489b-98d6-892c89fc90a4" xlink:href="fsk-20250331.xsd#fsk_ConsumerServicesSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_ConsumerServicesSectorMember_4997448b-4160-489b-98d6-892c89fc90a4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ConsumerStaplesDistributionRetailSectorMember_b3ee9552-2764-4103-be3b-1652d62c7a31" xlink:href="fsk-20250331.xsd#fsk_ConsumerStaplesDistributionRetailSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_ConsumerStaplesDistributionRetailSectorMember_b3ee9552-2764-4103-be3b-1652d62c7a31" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_cb436ce3-a006-40c9-b223-23b8bafb6c43" xlink:href="fsk-20250331.xsd#fsk_CreditOpportunitiesPartnersJVLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_cb436ce3-a006-40c9-b223-23b8bafb6c43" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EnergySectorMember_a801be63-742b-4721-ba20-aea1bd91daeb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_EnergySectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_us-gaap_EnergySectorMember_a801be63-742b-4721-ba20-aea1bd91daeb" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_EquityRealEstateInvestmentTrustsREITsSectorMember_16719c4c-97fc-4a1e-a2e7-257d38e37ace" xlink:href="fsk-20250331.xsd#fsk_EquityRealEstateInvestmentTrustsREITsSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_EquityRealEstateInvestmentTrustsREITsSectorMember_16719c4c-97fc-4a1e-a2e7-257d38e37ace" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialServicesSectorMember_e3a631a7-2140-4ab1-b572-5054d4910ba4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialServicesSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_us-gaap_FinancialServicesSectorMember_e3a631a7-2140-4ab1-b572-5054d4910ba4" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_FoodBeverageTobaccoSectorMember_c9e55f6f-0f22-42b4-afce-20f86a79ec95" xlink:href="fsk-20250331.xsd#fsk_FoodBeverageTobaccoSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_FoodBeverageTobaccoSectorMember_c9e55f6f-0f22-42b4-afce-20f86a79ec95" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_HealthCareEquipmentServicesSectorMember_8a20276f-bba0-4577-809a-c8e656535047" xlink:href="fsk-20250331.xsd#fsk_HealthCareEquipmentServicesSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_HealthCareEquipmentServicesSectorMember_8a20276f-bba0-4577-809a-c8e656535047" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_HouseholdPersonalProductsSectorMember_26e76824-07e5-44a5-91ed-d5a52727dbd6" xlink:href="fsk-20250331.xsd#fsk_HouseholdPersonalProductsSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_HouseholdPersonalProductsSectorMember_26e76824-07e5-44a5-91ed-d5a52727dbd6" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InsuranceSectorMember_2f8380f1-b53c-432a-94ad-5cbbc2052329" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InsuranceSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_us-gaap_InsuranceSectorMember_2f8380f1-b53c-432a-94ad-5cbbc2052329" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_MaterialsSectorMember_5762dba1-7d58-4439-be4f-54092035030a" xlink:href="fsk-20250331.xsd#fsk_MaterialsSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_MaterialsSectorMember_5762dba1-7d58-4439-be4f-54092035030a" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_MediaEntertainmentSectorMember_226d4bc6-ec6f-4466-b04e-cd1179073263" xlink:href="fsk-20250331.xsd#fsk_MediaEntertainmentSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_MediaEntertainmentSectorMember_226d4bc6-ec6f-4466-b04e-cd1179073263" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_PharmaceuticalsBiotechnologyLifeSciencesSectorMember_37922e02-e2d7-487a-97ea-3f6896c258a5" xlink:href="fsk-20250331.xsd#fsk_PharmaceuticalsBiotechnologyLifeSciencesSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_PharmaceuticalsBiotechnologyLifeSciencesSectorMember_37922e02-e2d7-487a-97ea-3f6896c258a5" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealEstateSectorMember_1f5c5f26-6dca-43b9-979a-c6601fb5c97b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RealEstateSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_us-gaap_RealEstateSectorMember_1f5c5f26-6dca-43b9-979a-c6601fb5c97b" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SoftwareServicesSectorMember_2ee5c80b-ceda-4176-b585-d29f9ad3801d" xlink:href="fsk-20250331.xsd#fsk_SoftwareServicesSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_SoftwareServicesSectorMember_2ee5c80b-ceda-4176-b585-d29f9ad3801d" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_TechnologyHardwareEquipmentSectorMember_610cb9ed-d1f6-4730-9eba-39e85ae52b91" xlink:href="fsk-20250331.xsd#fsk_TechnologyHardwareEquipmentSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_TechnologyHardwareEquipmentSectorMember_610cb9ed-d1f6-4730-9eba-39e85ae52b91" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_TelecommunicationServicesSectorMember_c82e9393-fd2e-4d44-98d6-ad18a3221fdf" xlink:href="fsk-20250331.xsd#fsk_TelecommunicationServicesSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_fsk_TelecommunicationServicesSectorMember_c82e9393-fd2e-4d44-98d6-ad18a3221fdf" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransportationSectorMember_1304b6ba-c03d-484e-bee3-cefff5066117" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_TransportationSectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquitySecuritiesIndustryMember_31437139-ff0a-41de-8bb5-55173a31f06a" xlink:to="loc_us-gaap_TransportationSectorMember_1304b6ba-c03d-484e-bee3-cefff5066117" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_f244d051-ecb9-4b90-b721-6b14e4193982" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryTable_3ef4d989-c079-4982-9494-06d97ac229bc" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_f244d051-ecb9-4b90-b721-6b14e4193982" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_f244d051-ecb9-4b90-b721-6b14e4193982_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_f244d051-ecb9-4b90-b721-6b14e4193982" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_f244d051-ecb9-4b90-b721-6b14e4193982_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_9f7ead99-66ca-4848-b7fa-7fbdf55a77de" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_f244d051-ecb9-4b90-b721-6b14e4193982" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_9f7ead99-66ca-4848-b7fa-7fbdf55a77de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentOwnedAtFairValueMember_bc949504-eb69-4851-bc72-57abf2e8dc3e" xlink:href="fsk-20250331.xsd#fsk_InvestmentOwnedAtFairValueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_9f7ead99-66ca-4848-b7fa-7fbdf55a77de" xlink:to="loc_fsk_InvestmentOwnedAtFairValueMember_bc949504-eb69-4851-bc72-57abf2e8dc3e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_7c2c1bef-9646-4e5e-853d-20bb6751c08a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryTable_3ef4d989-c079-4982-9494-06d97ac229bc" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_7c2c1bef-9646-4e5e-853d-20bb6751c08a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_7c2c1bef-9646-4e5e-853d-20bb6751c08a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_7c2c1bef-9646-4e5e-853d-20bb6751c08a" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_7c2c1bef-9646-4e5e-853d-20bb6751c08a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_3d544e75-01f8-45cb-a397-ec9b5f3b079d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_7c2c1bef-9646-4e5e-853d-20bb6751c08a" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_3d544e75-01f8-45cb-a397-ec9b5f3b079d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_IndustryConcentrationRiskMember_20ae2031-7876-46ad-a423-c25e8a1e2f05" xlink:href="fsk-20250331.xsd#fsk_IndustryConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_3d544e75-01f8-45cb-a397-ec9b5f3b079d" xlink:to="loc_fsk_IndustryConcentrationRiskMember_20ae2031-7876-46ad-a423-c25e8a1e2f05" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtFairValue_c948e595-b48f-47ec-8165-515e8ee69d95" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_ab08a2f3-c3e6-41dd-9561-709300f8e2a5" xlink:to="loc_us-gaap_InvestmentOwnedAtFairValue_c948e595-b48f-47ec-8165-515e8ee69d95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_97360e2c-ce47-46f1-af6e-b1763745aada" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_ab08a2f3-c3e6-41dd-9561-709300f8e2a5" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_97360e2c-ce47-46f1-af6e-b1763745aada" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/InvestmentPortfolioScheduleofBalanceSheetInformationforCOPJVDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#InvestmentPortfolioScheduleofBalanceSheetInformationforCOPJVDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/InvestmentPortfolioScheduleofBalanceSheetInformationforCOPJVDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_24cf647e-ad25-4c5f-b788-d397b4bd5642" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryTable_79438ef7-2929-41e4-a32c-0f27463b8c5b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_24cf647e-ad25-4c5f-b788-d397b4bd5642" xlink:to="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryTable_79438ef7-2929-41e4-a32c-0f27463b8c5b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis_1962af96-124c-40db-b830-763ce039340d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryTable_79438ef7-2929-41e4-a32c-0f27463b8c5b" xlink:to="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis_1962af96-124c-40db-b830-763ce039340d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_1962af96-124c-40db-b830-763ce039340d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis_1962af96-124c-40db-b830-763ce039340d" xlink:to="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_1962af96-124c-40db-b830-763ce039340d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_d53c6b38-af61-453b-9b7e-9d8a28107f68" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis_1962af96-124c-40db-b830-763ce039340d" xlink:to="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_d53c6b38-af61-453b-9b7e-9d8a28107f68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_c4cda698-a601-40b2-9547-4e0b022e5f13" xlink:href="fsk-20250331.xsd#fsk_CreditOpportunitiesPartnersJVLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_d53c6b38-af61-453b-9b7e-9d8a28107f68" xlink:to="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_c4cda698-a601-40b2-9547-4e0b022e5f13" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtFairValue_95540a07-a81c-4270-84ba-ba032cd711d7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_24cf647e-ad25-4c5f-b788-d397b4bd5642" xlink:to="loc_us-gaap_InvestmentOwnedAtFairValue_95540a07-a81c-4270-84ba-ba032cd711d7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_37c31e62-2a68-4e60-b251-80e62461877f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_24cf647e-ad25-4c5f-b788-d397b4bd5642" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_37c31e62-2a68-4e60-b251-80e62461877f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_fdea86c6-4177-4787-9aff-b2a6d915f883" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_24cf647e-ad25-4c5f-b788-d397b4bd5642" xlink:to="loc_us-gaap_Assets_fdea86c6-4177-4787-9aff-b2a6d915f883" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_d2026ba5-0551-4d3e-b4f4-127ed0372dbe" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtLongtermAndShorttermCombinedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_24cf647e-ad25-4c5f-b788-d397b4bd5642" xlink:to="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_d2026ba5-0551-4d3e-b4f4-127ed0372dbe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilities_41282792-1c66-4b11-8d82-9c14b3c380a2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_24cf647e-ad25-4c5f-b788-d397b4bd5642" xlink:to="loc_us-gaap_OtherLiabilities_41282792-1c66-4b11-8d82-9c14b3c380a2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_0df0f0f0-a8db-48c0-a113-1e6b841f40ca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_24cf647e-ad25-4c5f-b788-d397b4bd5642" xlink:to="loc_us-gaap_Liabilities_0df0f0f0-a8db-48c0-a113-1e6b841f40ca" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_3389f31f-f3a7-44a1-8dc6-1c542fcec43d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_24cf647e-ad25-4c5f-b788-d397b4bd5642" xlink:to="loc_us-gaap_StockholdersEquity_3389f31f-f3a7-44a1-8dc6-1c542fcec43d" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/InvestmentPortfolioScheduleofOperationsInformationforCOPJVDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#InvestmentPortfolioScheduleofOperationsInformationforCOPJVDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/InvestmentPortfolioScheduleofOperationsInformationforCOPJVDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_916ea0b2-c35d-44ba-8b9b-ae40af0a3cb5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryTable_3baa1904-c0bc-4721-b4cd-6b5925a266a1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_916ea0b2-c35d-44ba-8b9b-ae40af0a3cb5" xlink:to="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryTable_3baa1904-c0bc-4721-b4cd-6b5925a266a1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis_f4c13d11-5e30-41f1-b955-d2d875da0d71" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryTable_3baa1904-c0bc-4721-b4cd-6b5925a266a1" xlink:to="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis_f4c13d11-5e30-41f1-b955-d2d875da0d71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_f4c13d11-5e30-41f1-b955-d2d875da0d71_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis_f4c13d11-5e30-41f1-b955-d2d875da0d71" xlink:to="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_f4c13d11-5e30-41f1-b955-d2d875da0d71_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_765f5ea0-c4df-4e83-b11b-1c34acc22879" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryAxis_f4c13d11-5e30-41f1-b955-d2d875da0d71" xlink:to="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_765f5ea0-c4df-4e83-b11b-1c34acc22879" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_17f46936-098e-4873-9ca0-402c238132e2" xlink:href="fsk-20250331.xsd#fsk_CreditOpportunitiesPartnersJVLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryDomain_765f5ea0-c4df-4e83-b11b-1c34acc22879" xlink:to="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_17f46936-098e-4873-9ca0-402c238132e2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GrossInvestmentIncomeOperating_6d946051-860e-488d-aa6e-3ecc85520799" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GrossInvestmentIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_916ea0b2-c35d-44ba-8b9b-ae40af0a3cb5" xlink:to="loc_us-gaap_GrossInvestmentIncomeOperating_6d946051-860e-488d-aa6e-3ecc85520799" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_27220f84-aa11-42af-a066-24d604ee5a47" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_916ea0b2-c35d-44ba-8b9b-ae40af0a3cb5" xlink:to="loc_us-gaap_OperatingExpensesAbstract_27220f84-aa11-42af-a066-24d604ee5a47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_014452ea-07d7-483d-bafa-212e7b738fe0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_27220f84-aa11-42af-a066-24d604ee5a47" xlink:to="loc_us-gaap_InterestExpense_014452ea-07d7-483d-bafa-212e7b738fe0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoninterestExpenseTransferAgentAndCustodianFees_890f354a-2ff6-4fff-81f3-92ce4599c78a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NoninterestExpenseTransferAgentAndCustodianFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_27220f84-aa11-42af-a066-24d604ee5a47" xlink:to="loc_us-gaap_NoninterestExpenseTransferAgentAndCustodianFees_890f354a-2ff6-4fff-81f3-92ce4599c78a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AdministrativeServicesExpenses_63900ff3-6f60-4897-91db-3a54427c744b" xlink:href="fsk-20250331.xsd#fsk_AdministrativeServicesExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_27220f84-aa11-42af-a066-24d604ee5a47" xlink:to="loc_fsk_AdministrativeServicesExpenses_63900ff3-6f60-4897-91db-3a54427c744b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfessionalFees_9d9e1a65-17a3-4f4b-b82a-e01216eab4de" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProfessionalFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_27220f84-aa11-42af-a066-24d604ee5a47" xlink:to="loc_us-gaap_ProfessionalFees_9d9e1a65-17a3-4f4b-b82a-e01216eab4de" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherExpenses_1693087b-ecd3-42d9-89b6-989905975d95" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_27220f84-aa11-42af-a066-24d604ee5a47" xlink:to="loc_us-gaap_OtherExpenses_1693087b-ecd3-42d9-89b6-989905975d95" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyExpenseAfterReductionOfFeeWaiverAndReimbursement_cdccd20b-352b-4a6c-8b25-10966400fa36" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyExpenseAfterReductionOfFeeWaiverAndReimbursement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_27220f84-aa11-42af-a066-24d604ee5a47" xlink:to="loc_us-gaap_InvestmentCompanyExpenseAfterReductionOfFeeWaiverAndReimbursement_cdccd20b-352b-4a6c-8b25-10966400fa36" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetInvestmentIncome_fa21b5cc-6a3e-4885-9be7-edbc766329d7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_NetInvestmentIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_916ea0b2-c35d-44ba-8b9b-ae40af0a3cb5" xlink:to="loc_us-gaap_NetInvestmentIncome_fa21b5cc-6a3e-4885-9be7-edbc766329d7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RealizedAndUnrealizedGainLossInvestmentDerivativeAndForeignCurrencyTransactionOperatingAfterTax_6d090aec-ffd8-40bd-90da-9b41f059c65e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RealizedAndUnrealizedGainLossInvestmentDerivativeAndForeignCurrencyTransactionOperatingAfterTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_916ea0b2-c35d-44ba-8b9b-ae40af0a3cb5" xlink:to="loc_us-gaap_RealizedAndUnrealizedGainLossInvestmentDerivativeAndForeignCurrencyTransactionOperatingAfterTax_6d090aec-ffd8-40bd-90da-9b41f059c65e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_31cb1d24-dda4-4420-af8b-21261218d37a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentCompanyNonconsolidatedSubsidiaryLineItems_916ea0b2-c35d-44ba-8b9b-ae40af0a3cb5" xlink:to="loc_us-gaap_ProfitLoss_31cb1d24-dda4-4420-af8b-21261218d37a" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/FinancialInstrumentsScheduleofDerivativeInstrumentsFairValueDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#FinancialInstrumentsScheduleofDerivativeInstrumentsFairValueDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/FinancialInstrumentsScheduleofDerivativeInstrumentsFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_6a862a4d-d87d-4a32-b352-43fbd8e7f363" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_a104b99b-b6ca-46a6-871e-265441e43dc2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_6a862a4d-d87d-4a32-b352-43fbd8e7f363" xlink:to="loc_us-gaap_DerivativeTable_a104b99b-b6ca-46a6-871e-265441e43dc2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_51383e5c-0074-48e5-9ff2-5e5238aa8135" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_a104b99b-b6ca-46a6-871e-265441e43dc2" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_51383e5c-0074-48e5-9ff2-5e5238aa8135" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_51383e5c-0074-48e5-9ff2-5e5238aa8135_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_51383e5c-0074-48e5-9ff2-5e5238aa8135" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_51383e5c-0074-48e5-9ff2-5e5238aa8135_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_c28a1781-3fd6-4b8f-9e43-c5dcc25ec012" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_51383e5c-0074-48e5-9ff2-5e5238aa8135" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_c28a1781-3fd6-4b8f-9e43-c5dcc25ec012" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_2bb7d8a7-6900-44ed-9bcf-ec744db817fc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ForeignExchangeForwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_c28a1781-3fd6-4b8f-9e43-c5dcc25ec012" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_2bb7d8a7-6900-44ed-9bcf-ec744db817fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_7d00f230-0426-429a-8635-fdb56d725f35" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_6a862a4d-d87d-4a32-b352-43fbd8e7f363" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_7d00f230-0426-429a-8635-fdb56d725f35" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_ff5d7025-d594-4c0c-94d6-bc18b7434597" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_6a862a4d-d87d-4a32-b352-43fbd8e7f363" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_ff5d7025-d594-4c0c-94d6-bc18b7434597" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetAfterOffsetSubjectToMasterNettingArrangement_04375b2e-1e87-4284-824c-6d25a9a32aa8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeAssetAfterOffsetSubjectToMasterNettingArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_6a862a4d-d87d-4a32-b352-43fbd8e7f363" xlink:to="loc_us-gaap_DerivativeAssetAfterOffsetSubjectToMasterNettingArrangement_04375b2e-1e87-4284-824c-6d25a9a32aa8" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/FinancialInstrumentsScheduleofNetRealizedAndUnrealizedGainsAndLossesOnDerivativeInstrumentsDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#FinancialInstrumentsScheduleofNetRealizedAndUnrealizedGainsAndLossesOnDerivativeInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/FinancialInstrumentsScheduleofNetRealizedAndUnrealizedGainsAndLossesOnDerivativeInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_47d0793c-99f5-41ab-b3dd-2dda1249ee01" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeInstrumentsGainLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_ad6b969c-691f-40ee-8aaa-9e6950268018" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_47d0793c-99f5-41ab-b3dd-2dda1249ee01" xlink:to="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_ad6b969c-691f-40ee-8aaa-9e6950268018" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_bf508713-3916-419f-8db5-9d6beb383939" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipByIncomeStatementLocationByDerivativeInstrumentRiskTable_ad6b969c-691f-40ee-8aaa-9e6950268018" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_bf508713-3916-419f-8db5-9d6beb383939" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_bf508713-3916-419f-8db5-9d6beb383939_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_bf508713-3916-419f-8db5-9d6beb383939" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_bf508713-3916-419f-8db5-9d6beb383939_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_21750f9a-834d-4668-9033-bcc901262546" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_bf508713-3916-419f-8db5-9d6beb383939" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_21750f9a-834d-4668-9033-bcc901262546" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_c87d3fdf-7dd7-4aec-b75e-5308040fe55d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ForeignExchangeForwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_21750f9a-834d-4668-9033-bcc901262546" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_c87d3fdf-7dd7-4aec-b75e-5308040fe55d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfDerivatives_0ca822c4-82a4-45a6-ae61-1bc1fb886d96" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_GainLossOnSaleOfDerivatives"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_47d0793c-99f5-41ab-b3dd-2dda1249ee01" xlink:to="loc_us-gaap_GainLossOnSaleOfDerivatives_0ca822c4-82a4-45a6-ae61-1bc1fb886d96" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrealizedGainLossOnDerivatives_952205cb-7752-4000-873c-397ac2053765" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnrealizedGainLossOnDerivatives"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_47d0793c-99f5-41ab-b3dd-2dda1249ee01" xlink:to="loc_us-gaap_UnrealizedGainLossOnDerivatives_952205cb-7752-4000-873c-397ac2053765" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeGainLossOnDerivativeNet_de0ba26c-af8b-458d-83e7-2d7d6659a30e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeGainLossOnDerivativeNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsGainLossLineItems_47d0793c-99f5-41ab-b3dd-2dda1249ee01" xlink:to="loc_us-gaap_DerivativeGainLossOnDerivativeNet_de0ba26c-af8b-458d-83e7-2d7d6659a30e" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/FinancialInstrumentsScheduleofGrossAssetsAndLiabilitiesDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#FinancialInstrumentsScheduleofGrossAssetsAndLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/FinancialInstrumentsScheduleofGrossAssetsAndLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_2464c5c1-4e86-4444-9a14-82a707994713" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_07ce2485-4492-42eb-a7ab-07904e1ca8be" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_2464c5c1-4e86-4444-9a14-82a707994713" xlink:to="loc_us-gaap_DerivativeTable_07ce2485-4492-42eb-a7ab-07904e1ca8be" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_f51c036b-55f5-4dfe-8f14-c29875e2c22a" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_07ce2485-4492-42eb-a7ab-07904e1ca8be" xlink:to="loc_srt_CounterpartyNameAxis_f51c036b-55f5-4dfe-8f14-c29875e2c22a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_f51c036b-55f5-4dfe-8f14-c29875e2c22a_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_f51c036b-55f5-4dfe-8f14-c29875e2c22a" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_f51c036b-55f5-4dfe-8f14-c29875e2c22a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0de86f6e-5872-4c6c-95a5-be04c2a5b8ca" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_f51c036b-55f5-4dfe-8f14-c29875e2c22a" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0de86f6e-5872-4c6c-95a5-be04c2a5b8ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_JPMorganChaseBankMember_f6bfc6ea-eb16-48f9-9dd5-04923b35aacb" xlink:href="fsk-20250331.xsd#fsk_JPMorganChaseBankMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0de86f6e-5872-4c6c-95a5-be04c2a5b8ca" xlink:to="loc_fsk_JPMorganChaseBankMember_f6bfc6ea-eb16-48f9-9dd5-04923b35aacb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetsAbstract_0d0e354d-5223-423a-9bbd-5c07bca0e196" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeAssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_2464c5c1-4e86-4444-9a14-82a707994713" xlink:to="loc_us-gaap_DerivativeAssetsAbstract_0d0e354d-5223-423a-9bbd-5c07bca0e196" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_16a51ad3-0ea1-405f-b2b1-27d1e4089039" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeAssetsAbstract_0d0e354d-5223-423a-9bbd-5c07bca0e196" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_16a51ad3-0ea1-405f-b2b1-27d1e4089039" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetFairValueGrossLiability_f60bc2cb-9fd7-4ef9-839c-358d32601100" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeAssetFairValueGrossLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeAssetsAbstract_0d0e354d-5223-423a-9bbd-5c07bca0e196" xlink:to="loc_us-gaap_DerivativeAssetFairValueGrossLiability_f60bc2cb-9fd7-4ef9-839c-358d32601100" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralObligationToReturnSecurities_eb1d709f-1faa-4366-9ef8-d85a5a3c0ad4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeCollateralObligationToReturnSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeAssetsAbstract_0d0e354d-5223-423a-9bbd-5c07bca0e196" xlink:to="loc_us-gaap_DerivativeCollateralObligationToReturnSecurities_eb1d709f-1faa-4366-9ef8-d85a5a3c0ad4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralObligationToReturnCash_befe0d7d-2a0c-429e-9091-bbe575ba7bf7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeCollateralObligationToReturnCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeAssetsAbstract_0d0e354d-5223-423a-9bbd-5c07bca0e196" xlink:to="loc_us-gaap_DerivativeCollateralObligationToReturnCash_befe0d7d-2a0c-429e-9091-bbe575ba7bf7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral_b04d4300-36c7-4480-aa2e-0bd9f5a072c5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeAssetsAbstract_0d0e354d-5223-423a-9bbd-5c07bca0e196" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAssetAmountOffsetAgainstCollateral_b04d4300-36c7-4480-aa2e-0bd9f5a072c5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitiesAbstract_1031837e-4f8f-454d-8319-d8be0ecd20f9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_2464c5c1-4e86-4444-9a14-82a707994713" xlink:to="loc_us-gaap_DerivativeLiabilitiesAbstract_1031837e-4f8f-454d-8319-d8be0ecd20f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_95a120b4-dc8a-498a-a8c3-6f67720dfab4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLiabilitiesAbstract_1031837e-4f8f-454d-8319-d8be0ecd20f9" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_95a120b4-dc8a-498a-a8c3-6f67720dfab4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityFairValueGrossAsset_b026f405-2732-486d-93b7-302863db0b0c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLiabilityFairValueGrossAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLiabilitiesAbstract_1031837e-4f8f-454d-8319-d8be0ecd20f9" xlink:to="loc_us-gaap_DerivativeLiabilityFairValueGrossAsset_b026f405-2732-486d-93b7-302863db0b0c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedCollateralRightToReclaimSecurities_220647ce-9282-4059-b294-483967ad7328" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedCollateralRightToReclaimSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLiabilitiesAbstract_1031837e-4f8f-454d-8319-d8be0ecd20f9" xlink:to="loc_us-gaap_DerivativeLiabilitySecuritiesSoldUnderAgreementsToResellSecuritiesLoanedCollateralRightToReclaimSecurities_220647ce-9282-4059-b294-483967ad7328" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCollateralRightToReclaimCash_3c06b584-1763-4dce-ae4a-98308232afb3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeCollateralRightToReclaimCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLiabilitiesAbstract_1031837e-4f8f-454d-8319-d8be0ecd20f9" xlink:to="loc_us-gaap_DerivativeCollateralRightToReclaimCash_3c06b584-1763-4dce-ae4a-98308232afb3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral_c0e80070-a723-47ca-8a0a-5dfa15e11314" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLiabilitiesAbstract_1031837e-4f8f-454d-8319-d8be0ecd20f9" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiabilityAmountOffsetAgainstCollateral_c0e80070-a723-47ca-8a0a-5dfa15e11314" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/FinancialInstrumentsNarrativeDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#FinancialInstrumentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/FinancialInstrumentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_ba301a01-095f-4553-8500-76aabc24c81f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_bf28ee8c-d195-4a02-b068-9f9b5906ec47" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_ba301a01-095f-4553-8500-76aabc24c81f" xlink:to="loc_us-gaap_DerivativeTable_bf28ee8c-d195-4a02-b068-9f9b5906ec47" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_16633ac7-41ae-4baf-87b0-1e44c1aabe80" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_bf28ee8c-d195-4a02-b068-9f9b5906ec47" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_16633ac7-41ae-4baf-87b0-1e44c1aabe80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_16633ac7-41ae-4baf-87b0-1e44c1aabe80_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_16633ac7-41ae-4baf-87b0-1e44c1aabe80" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_16633ac7-41ae-4baf-87b0-1e44c1aabe80_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_cac51838-9af0-43be-801e-4626cbf84857" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_16633ac7-41ae-4baf-87b0-1e44c1aabe80" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_cac51838-9af0-43be-801e-4626cbf84857" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_11469dce-81d9-4424-9be1-15ff2e12c18e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ForeignExchangeForwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_cac51838-9af0-43be-801e-4626cbf84857" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_11469dce-81d9-4424-9be1-15ff2e12c18e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_d891949d-54a1-4252-befb-05b5f3ad97c1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_cac51838-9af0-43be-801e-4626cbf84857" xlink:to="loc_us-gaap_InterestRateSwapMember_d891949d-54a1-4252-befb-05b5f3ad97c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InterestRateSwapOneMember_c300d4b8-f7c2-4047-936a-ea70a5ba26f9" xlink:href="fsk-20250331.xsd#fsk_InterestRateSwapOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_d891949d-54a1-4252-befb-05b5f3ad97c1" xlink:to="loc_fsk_InterestRateSwapOneMember_c300d4b8-f7c2-4047-936a-ea70a5ba26f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InterestRateSwapTwoMember_c0a9b8f7-3d32-45db-9574-60ca82e27fab" xlink:href="fsk-20250331.xsd#fsk_InterestRateSwapTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_d891949d-54a1-4252-befb-05b5f3ad97c1" xlink:to="loc_fsk_InterestRateSwapTwoMember_c0a9b8f7-3d32-45db-9574-60ca82e27fab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InterestRateSwapThreeMember_8e79b4c7-9667-4027-8134-f60f287ac381" xlink:href="fsk-20250331.xsd#fsk_InterestRateSwapThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_d891949d-54a1-4252-befb-05b5f3ad97c1" xlink:to="loc_fsk_InterestRateSwapThreeMember_8e79b4c7-9667-4027-8134-f60f287ac381" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InterestRateSwapFourMember_02549900-e074-4dff-886b-bba3c6eaeab3" xlink:href="fsk-20250331.xsd#fsk_InterestRateSwapFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_d891949d-54a1-4252-befb-05b5f3ad97c1" xlink:to="loc_fsk_InterestRateSwapFourMember_02549900-e074-4dff-886b-bba3c6eaeab3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_aaf869b5-d061-4baa-9f41-0d04b0d848c1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_bf28ee8c-d195-4a02-b068-9f9b5906ec47" xlink:to="loc_us-gaap_DebtInstrumentAxis_aaf869b5-d061-4baa-9f41-0d04b0d848c1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_aaf869b5-d061-4baa-9f41-0d04b0d848c1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_aaf869b5-d061-4baa-9f41-0d04b0d848c1" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_aaf869b5-d061-4baa-9f41-0d04b0d848c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_90a211de-78e8-42cb-9c5b-f203e8ba314c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_aaf869b5-d061-4baa-9f41-0d04b0d848c1" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_90a211de-78e8-42cb-9c5b-f203e8ba314c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A6.875UnsecuredNotesDue2029Member_2bd4ff44-2a0c-4bb6-9afb-823105072eff" xlink:href="fsk-20250331.xsd#fsk_A6.875UnsecuredNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_90a211de-78e8-42cb-9c5b-f203e8ba314c" xlink:to="loc_fsk_A6.875UnsecuredNotesDue2029Member_2bd4ff44-2a0c-4bb6-9afb-823105072eff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A6.125UnsecuredNotesDue2030Member_9bff0722-f6bd-41fd-b1d8-71cd208a0731" xlink:href="fsk-20250331.xsd#fsk_A6.125UnsecuredNotesDue2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_90a211de-78e8-42cb-9c5b-f203e8ba314c" xlink:to="loc_fsk_A6.125UnsecuredNotesDue2030Member_9bff0722-f6bd-41fd-b1d8-71cd208a0731" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_71de9524-1bc4-4d60-9aea-506e5d3140eb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_bf28ee8c-d195-4a02-b068-9f9b5906ec47" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_71de9524-1bc4-4d60-9aea-506e5d3140eb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_71de9524-1bc4-4d60-9aea-506e5d3140eb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_71de9524-1bc4-4d60-9aea-506e5d3140eb" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_71de9524-1bc4-4d60-9aea-506e5d3140eb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_1a01dc46-26c0-464d-bbed-84080bf6f6e8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_71de9524-1bc4-4d60-9aea-506e5d3140eb" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_1a01dc46-26c0-464d-bbed-84080bf6f6e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_74980f3f-b920-43ef-876a-417a0e716d30" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_1a01dc46-26c0-464d-bbed-84080bf6f6e8" xlink:to="loc_us-gaap_UnsecuredDebtMember_74980f3f-b920-43ef-876a-417a0e716d30" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_DerivativeAssetAverageNotionalBalance_2e55ed95-a961-4da6-8710-dbc3af6f7f9b" xlink:href="fsk-20250331.xsd#fsk_DerivativeAssetAverageNotionalBalance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_ba301a01-095f-4553-8500-76aabc24c81f" xlink:to="loc_fsk_DerivativeAssetAverageNotionalBalance_2e55ed95-a961-4da6-8710-dbc3af6f7f9b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_421e4d63-bdb1-4677-a8b6-a641343ec3a8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_ba301a01-095f-4553-8500-76aabc24c81f" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_421e4d63-bdb1-4677-a8b6-a641343ec3a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_4f4f35cc-735c-46f3-8566-63133836102b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_ba301a01-095f-4553-8500-76aabc24c81f" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_4f4f35cc-735c-46f3-8566-63133836102b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_3464cb10-4d35-46bd-83b2-6c60c69da6de" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_ba301a01-095f-4553-8500-76aabc24c81f" xlink:to="loc_us-gaap_DerivativeNotionalAmount_3464cb10-4d35-46bd-83b2-6c60c69da6de" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFixedInterestRate_27de2e17-46aa-4db6-bfd4-8ee4acd2dc0a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_ba301a01-095f-4553-8500-76aabc24c81f" xlink:to="loc_us-gaap_DerivativeFixedInterestRate_27de2e17-46aa-4db6-bfd4-8ee4acd2dc0a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeVariableInterestRate_af756937-96e5-4e61-b2e4-823c6d3ff2dc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeVariableInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_ba301a01-095f-4553-8500-76aabc24c81f" xlink:to="loc_us-gaap_DerivativeVariableInterestRate_af756937-96e5-4e61-b2e4-823c6d3ff2dc" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/FinancialInstrumentsScheduleofDerivativeInstrumentsFairValueDetails_1" xlink:type="simple" xlink:href="fsk-20250331.xsd#FinancialInstrumentsScheduleofDerivativeInstrumentsFairValueDetails_1"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/FinancialInstrumentsScheduleofDerivativeInstrumentsFairValueDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_f28f6bef-bf7a-406c-9572-f9602cb3f2a3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_9d25ffbb-9b2b-4d4e-9a56-319baab7efb8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_f28f6bef-bf7a-406c-9572-f9602cb3f2a3" xlink:to="loc_us-gaap_DerivativeTable_9d25ffbb-9b2b-4d4e-9a56-319baab7efb8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_2b43f4a2-e74d-4fbf-a83f-9d683a2799d4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_9d25ffbb-9b2b-4d4e-9a56-319baab7efb8" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_2b43f4a2-e74d-4fbf-a83f-9d683a2799d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_2b43f4a2-e74d-4fbf-a83f-9d683a2799d4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_2b43f4a2-e74d-4fbf-a83f-9d683a2799d4" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_2b43f4a2-e74d-4fbf-a83f-9d683a2799d4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_55e76710-0417-435d-ac93-59717a24e4e5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_2b43f4a2-e74d-4fbf-a83f-9d683a2799d4" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_55e76710-0417-435d-ac93-59717a24e4e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_528a4d5d-fe71-46a9-8213-e802847d1b68" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_55e76710-0417-435d-ac93-59717a24e4e5" xlink:to="loc_us-gaap_InterestRateSwapMember_528a4d5d-fe71-46a9-8213-e802847d1b68" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InterestRateSwapOneMember_b6d79d06-cdd9-4075-bf49-5b6fb6704d25" xlink:href="fsk-20250331.xsd#fsk_InterestRateSwapOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_528a4d5d-fe71-46a9-8213-e802847d1b68" xlink:to="loc_fsk_InterestRateSwapOneMember_b6d79d06-cdd9-4075-bf49-5b6fb6704d25" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InterestRateSwapTwoMember_632067d9-6615-49c3-80bf-1fde10382331" xlink:href="fsk-20250331.xsd#fsk_InterestRateSwapTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_528a4d5d-fe71-46a9-8213-e802847d1b68" xlink:to="loc_fsk_InterestRateSwapTwoMember_632067d9-6615-49c3-80bf-1fde10382331" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InterestRateSwapThreeMember_161c95dd-77df-4827-a677-7944a85ca35f" xlink:href="fsk-20250331.xsd#fsk_InterestRateSwapThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_528a4d5d-fe71-46a9-8213-e802847d1b68" xlink:to="loc_fsk_InterestRateSwapThreeMember_161c95dd-77df-4827-a677-7944a85ca35f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InterestRateSwapFourMember_2a7d32e8-a605-4220-b8fa-cab9d4fa7bfb" xlink:href="fsk-20250331.xsd#fsk_InterestRateSwapFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InterestRateSwapMember_528a4d5d-fe71-46a9-8213-e802847d1b68" xlink:to="loc_fsk_InterestRateSwapFourMember_2a7d32e8-a605-4220-b8fa-cab9d4fa7bfb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_76046498-9826-4f48-9b27-14d65fad1f3f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_9d25ffbb-9b2b-4d4e-9a56-319baab7efb8" xlink:to="loc_us-gaap_DebtInstrumentAxis_76046498-9826-4f48-9b27-14d65fad1f3f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_76046498-9826-4f48-9b27-14d65fad1f3f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_76046498-9826-4f48-9b27-14d65fad1f3f" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_76046498-9826-4f48-9b27-14d65fad1f3f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_ead00c57-56b1-424b-a394-8e4014820408" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_76046498-9826-4f48-9b27-14d65fad1f3f" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_ead00c57-56b1-424b-a394-8e4014820408" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A6.875UnsecuredNotesDue2029Member_210cced4-06df-460b-9297-bab24a664b44" xlink:href="fsk-20250331.xsd#fsk_A6.875UnsecuredNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ead00c57-56b1-424b-a394-8e4014820408" xlink:to="loc_fsk_A6.875UnsecuredNotesDue2029Member_210cced4-06df-460b-9297-bab24a664b44" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A6.125UnsecuredNotesDue2029Member_476da756-1375-41a9-891f-9e6ba3ce7d82" xlink:href="fsk-20250331.xsd#fsk_A6.125UnsecuredNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ead00c57-56b1-424b-a394-8e4014820408" xlink:to="loc_fsk_A6.125UnsecuredNotesDue2029Member_476da756-1375-41a9-891f-9e6ba3ce7d82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_e90fc8c0-319b-42f5-b713-8b66ebcf4ec2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_9d25ffbb-9b2b-4d4e-9a56-319baab7efb8" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_e90fc8c0-319b-42f5-b713-8b66ebcf4ec2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_e90fc8c0-319b-42f5-b713-8b66ebcf4ec2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_e90fc8c0-319b-42f5-b713-8b66ebcf4ec2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_e90fc8c0-319b-42f5-b713-8b66ebcf4ec2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_7473be77-8727-4322-956c-647e70e091c2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_e90fc8c0-319b-42f5-b713-8b66ebcf4ec2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_7473be77-8727-4322-956c-647e70e091c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_a6f91fb1-3c18-4e14-b8dc-a02edde2f63a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_7473be77-8727-4322-956c-647e70e091c2" xlink:to="loc_us-gaap_UnsecuredDebtMember_a6f91fb1-3c18-4e14-b8dc-a02edde2f63a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_a8d8ace2-3101-491d-99f1-5711f1b88c8f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_f28f6bef-bf7a-406c-9572-f9602cb3f2a3" xlink:to="loc_us-gaap_DerivativeNotionalAmount_a8d8ace2-3101-491d-99f1-5711f1b88c8f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_d5695a47-ee07-45d9-9422-31b64152ed17" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_f28f6bef-bf7a-406c-9572-f9602cb3f2a3" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_d5695a47-ee07-45d9-9422-31b64152ed17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_79ad45b3-b6a0-40b4-8580-af7a0d08b3b3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFairValueOfDerivativeLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_f28f6bef-bf7a-406c-9572-f9602cb3f2a3" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeLiability_79ad45b3-b6a0-40b4-8580-af7a0d08b3b3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_62f65440-89fb-4574-b21f-b102918e9b54" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_f28f6bef-bf7a-406c-9572-f9602cb3f2a3" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_62f65440-89fb-4574-b21f-b102918e9b54" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/FairValueofFinancialInstrumentsScheduleofFairValueHierarchyDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#FairValueofFinancialInstrumentsScheduleofFairValueHierarchyDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/FairValueofFinancialInstrumentsScheduleofFairValueHierarchyDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6bf17b51-ed33-42ae-ac83-252d73597c4a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_cae2c279-63aa-4530-8379-047b745a48d7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6bf17b51-ed33-42ae-ac83-252d73597c4a" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_cae2c279-63aa-4530-8379-047b745a48d7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8c11fec3-0a52-4fce-b4c8-b45c523986c4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_cae2c279-63aa-4530-8379-047b745a48d7" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8c11fec3-0a52-4fce-b4c8-b45c523986c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8c11fec3-0a52-4fce-b4c8-b45c523986c4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8c11fec3-0a52-4fce-b4c8-b45c523986c4" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8c11fec3-0a52-4fce-b4c8-b45c523986c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f3d1bbb0-4e83-48d6-b3ad-880fad2359b7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8c11fec3-0a52-4fce-b4c8-b45c523986c4" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f3d1bbb0-4e83-48d6-b3ad-880fad2359b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_5c800108-dd5c-4239-9d58-420176b68743" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f3d1bbb0-4e83-48d6-b3ad-880fad2359b7" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_5c800108-dd5c-4239-9d58-420176b68743" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_fbc438a4-5348-4c66-bf7b-b66e5703f0b3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f3d1bbb0-4e83-48d6-b3ad-880fad2359b7" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_fbc438a4-5348-4c66-bf7b-b66e5703f0b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_2bbdf389-652f-4db3-af5b-9f50befbb101" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f3d1bbb0-4e83-48d6-b3ad-880fad2359b7" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_2bbdf389-652f-4db3-af5b-9f50befbb101" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_7cbed674-9509-4719-9bfd-5e0c53023e59" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f3d1bbb0-4e83-48d6-b3ad-880fad2359b7" xlink:to="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_7cbed674-9509-4719-9bfd-5e0c53023e59" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtFairValue_efb06873-5c9e-4e05-b7d2-cf57696ee2d4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6bf17b51-ed33-42ae-ac83-252d73597c4a" xlink:to="loc_us-gaap_InvestmentOwnedAtFairValue_efb06873-5c9e-4e05-b7d2-cf57696ee2d4" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/FairValueofFinancialInstrumentsScheduleofRollForwardLevelIIIDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#FairValueofFinancialInstrumentsScheduleofRollForwardLevelIIIDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/FairValueofFinancialInstrumentsScheduleofRollForwardLevelIIIDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_4ea032a9-cfe4-42df-8dfa-38f1f7d81cff" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ba99b727-df1c-4393-bb7c-c8d8f0dec72d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_4ea032a9-cfe4-42df-8dfa-38f1f7d81cff" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ba99b727-df1c-4393-bb7c-c8d8f0dec72d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_3664bc1e-02c6-4231-844c-eaaae0c8644e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ba99b727-df1c-4393-bb7c-c8d8f0dec72d" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_3664bc1e-02c6-4231-844c-eaaae0c8644e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_3664bc1e-02c6-4231-844c-eaaae0c8644e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_3664bc1e-02c6-4231-844c-eaaae0c8644e" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_3664bc1e-02c6-4231-844c-eaaae0c8644e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_bb98f942-c5b1-43d2-8687-1c2ce905fc4a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_3664bc1e-02c6-4231-844c-eaaae0c8644e" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_bb98f942-c5b1-43d2-8687-1c2ce905fc4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SeniorSecuredLoansFirstLienMember_a80c37cf-0990-4bb8-b5a3-593d310ffd5d" xlink:href="fsk-20250331.xsd#fsk_SeniorSecuredLoansFirstLienMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_bb98f942-c5b1-43d2-8687-1c2ce905fc4a" xlink:to="loc_fsk_SeniorSecuredLoansFirstLienMember_a80c37cf-0990-4bb8-b5a3-593d310ffd5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SeniorSecuredLoansSecondLienMember_d5c06d0d-7dee-4186-8358-d2041e5bf270" xlink:href="fsk-20250331.xsd#fsk_SeniorSecuredLoansSecondLienMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_bb98f942-c5b1-43d2-8687-1c2ce905fc4a" xlink:to="loc_fsk_SeniorSecuredLoansSecondLienMember_d5c06d0d-7dee-4186-8358-d2041e5bf270" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_DebtSecuritiesOtherSeniorSecuredDebtMember_7f7d4d6c-a40a-4cb2-9bc9-7a1834c3810b" xlink:href="fsk-20250331.xsd#fsk_DebtSecuritiesOtherSeniorSecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_bb98f942-c5b1-43d2-8687-1c2ce905fc4a" xlink:to="loc_fsk_DebtSecuritiesOtherSeniorSecuredDebtMember_7f7d4d6c-a40a-4cb2-9bc9-7a1834c3810b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedDebtMember_70421a9e-a97c-4bfa-8102-a8191522cbc3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubordinatedDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_bb98f942-c5b1-43d2-8687-1c2ce905fc4a" xlink:to="loc_us-gaap_SubordinatedDebtMember_70421a9e-a97c-4bfa-8102-a8191522cbc3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AssetBasedFinanceMember_7bcf147c-dc37-45d1-a2a2-342756bcfc3e" xlink:href="fsk-20250331.xsd#fsk_AssetBasedFinanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_bb98f942-c5b1-43d2-8687-1c2ce905fc4a" xlink:to="loc_fsk_AssetBasedFinanceMember_7bcf147c-dc37-45d1-a2a2-342756bcfc3e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_EquityOtherMember_fd589b58-a24d-436b-a9be-9b9e4f8ba1aa" xlink:href="fsk-20250331.xsd#fsk_EquityOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_bb98f942-c5b1-43d2-8687-1c2ce905fc4a" xlink:to="loc_fsk_EquityOtherMember_fd589b58-a24d-436b-a9be-9b9e4f8ba1aa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_4ff2294c-5d1d-444d-a9d2-6f467290723c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_ba99b727-df1c-4393-bb7c-c8d8f0dec72d" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_4ff2294c-5d1d-444d-a9d2-6f467290723c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_4ff2294c-5d1d-444d-a9d2-6f467290723c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_4ff2294c-5d1d-444d-a9d2-6f467290723c" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_4ff2294c-5d1d-444d-a9d2-6f467290723c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_9d8f11b4-c942-4400-9c9b-b9fcb1b6ac01" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_4ff2294c-5d1d-444d-a9d2-6f467290723c" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_9d8f11b4-c942-4400-9c9b-b9fcb1b6ac01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_DebtAndEquitySecuritiesRealizedGainLossMember_3f929c06-2835-4628-8c50-d27f49eae9d8" xlink:href="fsk-20250331.xsd#fsk_DebtAndEquitySecuritiesRealizedGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_9d8f11b4-c942-4400-9c9b-b9fcb1b6ac01" xlink:to="loc_fsk_DebtAndEquitySecuritiesRealizedGainLossMember_3f929c06-2835-4628-8c50-d27f49eae9d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_DebtAndEquitySecuritiesUnrealizedGainLossMember_d994c8bd-15b9-4356-9f33-249cc285a685" xlink:href="fsk-20250331.xsd#fsk_DebtAndEquitySecuritiesUnrealizedGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_9d8f11b4-c942-4400-9c9b-b9fcb1b6ac01" xlink:to="loc_fsk_DebtAndEquitySecuritiesUnrealizedGainLossMember_d994c8bd-15b9-4356-9f33-249cc285a685" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_6bd8f3d0-b18f-408a-860d-07ccff7a106b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_4ea032a9-cfe4-42df-8dfa-38f1f7d81cff" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_6bd8f3d0-b18f-408a-860d-07ccff7a106b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_0967519f-a533-424d-9e4f-658e34806e87" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_6bd8f3d0-b18f-408a-860d-07ccff7a106b" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_0967519f-a533-424d-9e4f-658e34806e87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_d5034e53-09b4-4dfa-80e8-e5a197fd5e2e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_6bd8f3d0-b18f-408a-860d-07ccff7a106b" xlink:to="loc_us-gaap_AccretionAmortizationOfDiscountsAndPremiumsInvestments_d5034e53-09b4-4dfa-80e8-e5a197fd5e2e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_1bcd38a4-e97a-48cf-a3b3-0ccf3b55b180" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_6bd8f3d0-b18f-408a-860d-07ccff7a106b" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_1bcd38a4-e97a-48cf-a3b3-0ccf3b55b180" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_96a02d85-6913-467c-82c9-1d755b1d1112" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_6bd8f3d0-b18f-408a-860d-07ccff7a106b" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_96a02d85-6913-467c-82c9-1d755b1d1112" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisPaidInKindInterest_684b8b32-f825-494e-b3a8-22877e354f03" xlink:href="fsk-20250331.xsd#fsk_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisPaidInKindInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_6bd8f3d0-b18f-408a-860d-07ccff7a106b" xlink:to="loc_fsk_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisPaidInKindInterest_684b8b32-f825-494e-b3a8-22877e354f03" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisSalesAndRepayments_0b839915-f56e-44de-a802-9ed8b50b1117" xlink:href="fsk-20250331.xsd#fsk_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisSalesAndRepayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_6bd8f3d0-b18f-408a-860d-07ccff7a106b" xlink:to="loc_fsk_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisSalesAndRepayments_0b839915-f56e-44de-a802-9ed8b50b1117" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3_696e6b63-1555-4b9a-82cd-3466dc1e6929" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_6bd8f3d0-b18f-408a-860d-07ccff7a106b" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersIntoLevel3_696e6b63-1555-4b9a-82cd-3466dc1e6929" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3_f7d4a9af-8c78-48be-9b1b-2822805ab62b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_6bd8f3d0-b18f-408a-860d-07ccff7a106b" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3_f7d4a9af-8c78-48be-9b1b-2822805ab62b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_e95c8c1e-cdb5-4460-be87-abd253358f37" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_02fe2de6-c89c-4ec0-81a0-f9abf7096ccf" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_4ea032a9-cfe4-42df-8dfa-38f1f7d81cff" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_02fe2de6-c89c-4ec0-81a0-f9abf7096ccf" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/FairValueofFinancialInstrumentsScheduleofUnobservableInputsDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#FairValueofFinancialInstrumentsScheduleofUnobservableInputsDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/FairValueofFinancialInstrumentsScheduleofUnobservableInputsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_de91d2f2-e634-46b1-9eff-f407c10190c0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_c98ebec0-e91c-4b2c-a3ac-14048713edbd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_de91d2f2-e634-46b1-9eff-f407c10190c0" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_c98ebec0-e91c-4b2c-a3ac-14048713edbd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3a43838f-3e32-4996-8b28-f48e91b10b91" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_c98ebec0-e91c-4b2c-a3ac-14048713edbd" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3a43838f-3e32-4996-8b28-f48e91b10b91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_3a43838f-3e32-4996-8b28-f48e91b10b91_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3a43838f-3e32-4996-8b28-f48e91b10b91" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_3a43838f-3e32-4996-8b28-f48e91b10b91_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9c7e13d7-df18-4129-ae65-b043bd42ac49" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_3a43838f-3e32-4996-8b28-f48e91b10b91" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9c7e13d7-df18-4129-ae65-b043bd42ac49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_31f6483e-16fc-4f59-8144-b60c0e8a2570" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_9c7e13d7-df18-4129-ae65-b043bd42ac49" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_31f6483e-16fc-4f59-8144-b60c0e8a2570" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_814f6fa9-61a5-4cf4-80ed-182d86941dde" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_c98ebec0-e91c-4b2c-a3ac-14048713edbd" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_814f6fa9-61a5-4cf4-80ed-182d86941dde" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_814f6fa9-61a5-4cf4-80ed-182d86941dde_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_814f6fa9-61a5-4cf4-80ed-182d86941dde" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_814f6fa9-61a5-4cf4-80ed-182d86941dde_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_1950741a-a12e-40e5-bcf4-72d85ee5d593" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_814f6fa9-61a5-4cf4-80ed-182d86941dde" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_1950741a-a12e-40e5-bcf4-72d85ee5d593" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_ce7282e2-4672-4cfd-ae1e-b8c55afd3019" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_1950741a-a12e-40e5-bcf4-72d85ee5d593" xlink:to="loc_us-gaap_SeniorNotesMember_ce7282e2-4672-4cfd-ae1e-b8c55afd3019" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubordinatedDebtMember_6ae35c60-c08a-438e-a918-ed50b93641a4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubordinatedDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_1950741a-a12e-40e5-bcf4-72d85ee5d593" xlink:to="loc_us-gaap_SubordinatedDebtMember_6ae35c60-c08a-438e-a918-ed50b93641a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AssetBasedFinanceMember_c15cac2e-c2cf-40ff-a1fe-9805cad76215" xlink:href="fsk-20250331.xsd#fsk_AssetBasedFinanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_1950741a-a12e-40e5-bcf4-72d85ee5d593" xlink:to="loc_fsk_AssetBasedFinanceMember_c15cac2e-c2cf-40ff-a1fe-9805cad76215" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_EquityOtherMember_67039b81-b333-4b04-9f11-4bb7b3f93641" xlink:href="fsk-20250331.xsd#fsk_EquityOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_1950741a-a12e-40e5-bcf4-72d85ee5d593" xlink:to="loc_fsk_EquityOtherMember_67039b81-b333-4b04-9f11-4bb7b3f93641" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueAxis_e63dfc6b-c1f9-4383-9ad0-0ccdabfb1daa" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_c98ebec0-e91c-4b2c-a3ac-14048713edbd" xlink:to="loc_us-gaap_ValuationTechniqueAxis_e63dfc6b-c1f9-4383-9ad0-0ccdabfb1daa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_e63dfc6b-c1f9-4383-9ad0-0ccdabfb1daa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ValuationTechniqueAxis_e63dfc6b-c1f9-4383-9ad0-0ccdabfb1daa" xlink:to="loc_us-gaap_ValuationTechniqueDomain_e63dfc6b-c1f9-4383-9ad0-0ccdabfb1daa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDomain_fa37c1ce-1718-4a24-a095-abbfe0531e4e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ValuationTechniqueAxis_e63dfc6b-c1f9-4383-9ad0-0ccdabfb1daa" xlink:to="loc_us-gaap_ValuationTechniqueDomain_fa37c1ce-1718-4a24-a095-abbfe0531e4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_7b99e490-c686-4e66-9940-e1f160ea2c30" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueDiscountedCashFlowMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_fa37c1ce-1718-4a24-a095-abbfe0531e4e" xlink:to="loc_us-gaap_ValuationTechniqueDiscountedCashFlowMember_7b99e490-c686-4e66-9940-e1f160ea2c30" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ValuationWaterfallApproachMember_5d90e4e6-af37-41bd-8766-2603ee5b33d6" xlink:href="fsk-20250331.xsd#fsk_ValuationWaterfallApproachMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_fa37c1ce-1718-4a24-a095-abbfe0531e4e" xlink:to="loc_fsk_ValuationWaterfallApproachMember_5d90e4e6-af37-41bd-8766-2603ee5b33d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ValuationOtherApproachMember_b9aa7b73-2b73-470a-aeae-b3013386c4b4" xlink:href="fsk-20250331.xsd#fsk_ValuationOtherApproachMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_fa37c1ce-1718-4a24-a095-abbfe0531e4e" xlink:to="loc_fsk_ValuationOtherApproachMember_b9aa7b73-2b73-470a-aeae-b3013386c4b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostApproachValuationTechniqueMember_47238f28-0ffb-4bd6-8d71-eeac3d83b062" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CostApproachValuationTechniqueMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_fa37c1ce-1718-4a24-a095-abbfe0531e4e" xlink:to="loc_us-gaap_CostApproachValuationTechniqueMember_47238f28-0ffb-4bd6-8d71-eeac3d83b062" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ValuationIndicativeDealerQuotesApproachMember_503fae8b-b163-416f-b656-0d6eb72614e2" xlink:href="fsk-20250331.xsd#fsk_ValuationIndicativeDealerQuotesApproachMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_fa37c1ce-1718-4a24-a095-abbfe0531e4e" xlink:to="loc_fsk_ValuationIndicativeDealerQuotesApproachMember_503fae8b-b163-416f-b656-0d6eb72614e2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ValuationTechniqueOptionPricingModelMember_dfe2a0fd-312a-4f77-9d05-e3f61ac0cffd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ValuationTechniqueOptionPricingModelMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ValuationTechniqueDomain_fa37c1ce-1718-4a24-a095-abbfe0531e4e" xlink:to="loc_us-gaap_ValuationTechniqueOptionPricingModelMember_dfe2a0fd-312a-4f77-9d05-e3f61ac0cffd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_8dc90882-fe06-4b00-8fd0-3783badf6628" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_c98ebec0-e91c-4b2c-a3ac-14048713edbd" xlink:to="loc_srt_RangeAxis_8dc90882-fe06-4b00-8fd0-3783badf6628" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_8dc90882-fe06-4b00-8fd0-3783badf6628_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_8dc90882-fe06-4b00-8fd0-3783badf6628" xlink:to="loc_srt_RangeMember_8dc90882-fe06-4b00-8fd0-3783badf6628_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b9dddace-a0b9-4717-b54d-a707251e0729" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_8dc90882-fe06-4b00-8fd0-3783badf6628" xlink:to="loc_srt_RangeMember_b9dddace-a0b9-4717-b54d-a707251e0729" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_9905aa68-3817-404c-ab8b-7da888741328" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_b9dddace-a0b9-4717-b54d-a707251e0729" xlink:to="loc_srt_MinimumMember_9905aa68-3817-404c-ab8b-7da888741328" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_bc42a5e4-d01b-45a6-b880-5cc0873e0b3e" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_b9dddace-a0b9-4717-b54d-a707251e0729" xlink:to="loc_srt_MaximumMember_bc42a5e4-d01b-45a6-b880-5cc0873e0b3e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_95ded750-972d-4bf0-a19c-e72758d79376" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_WeightedAverageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_b9dddace-a0b9-4717-b54d-a707251e0729" xlink:to="loc_srt_WeightedAverageMember_95ded750-972d-4bf0-a19c-e72758d79376" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_34355889-8397-4d4b-9ab3-a24cb084a636" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_c98ebec0-e91c-4b2c-a3ac-14048713edbd" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_34355889-8397-4d4b-9ab3-a24cb084a636" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_34355889-8397-4d4b-9ab3-a24cb084a636_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_34355889-8397-4d4b-9ab3-a24cb084a636" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_34355889-8397-4d4b-9ab3-a24cb084a636_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_98b6e98b-8f82-4c68-8558-1bfc6e75654f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_34355889-8397-4d4b-9ab3-a24cb084a636" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_98b6e98b-8f82-4c68-8558-1bfc6e75654f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_fba8e0ba-bed3-4851-a13e-fdf23a8a7bed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_98b6e98b-8f82-4c68-8558-1bfc6e75654f" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_fba8e0ba-bed3-4851-a13e-fdf23a8a7bed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputEbitdaMultipleMember_f2b3e199-08a2-4506-aee3-80600c8ca9cd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_MeasurementInputEbitdaMultipleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_98b6e98b-8f82-4c68-8558-1bfc6e75654f" xlink:to="loc_us-gaap_MeasurementInputEbitdaMultipleMember_f2b3e199-08a2-4506-aee3-80600c8ca9cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_MeasurementInputEquityIlliquidityDiscountMember_e65e0f32-c9cb-4fc4-8804-19ce11a87087" xlink:href="fsk-20250331.xsd#fsk_MeasurementInputEquityIlliquidityDiscountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_98b6e98b-8f82-4c68-8558-1bfc6e75654f" xlink:to="loc_fsk_MeasurementInputEquityIlliquidityDiscountMember_e65e0f32-c9cb-4fc4-8804-19ce11a87087" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedAtFairValue_8b5f7fe7-26f4-4137-b42a-4c9a607c9cf2" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_de91d2f2-e634-46b1-9eff-f407c10190c0" xlink:to="loc_us-gaap_InvestmentOwnedAtFairValue_8b5f7fe7-26f4-4137-b42a-4c9a607c9cf2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyInvestmentOwnedFairValueMeasurementInput_46c5ca98-dc54-44bb-83d9-27f0d570bebb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyInvestmentOwnedFairValueMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_de91d2f2-e634-46b1-9eff-f407c10190c0" xlink:to="loc_us-gaap_InvestmentCompanyInvestmentOwnedFairValueMeasurementInput_46c5ca98-dc54-44bb-83d9-27f0d570bebb" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/FinancingArrangementsNarrativeDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#FinancingArrangementsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/FinancingArrangementsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_ba17b9f3-da5a-445c-8398-9a500146b1d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:to="loc_us-gaap_DebtInstrumentTable_ba17b9f3-da5a-445c-8398-9a500146b1d6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_424cd41d-ff4a-4cc1-b826-00e9af7e74d6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ba17b9f3-da5a-445c-8398-9a500146b1d6" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_424cd41d-ff4a-4cc1-b826-00e9af7e74d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_424cd41d-ff4a-4cc1-b826-00e9af7e74d6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_424cd41d-ff4a-4cc1-b826-00e9af7e74d6" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_424cd41d-ff4a-4cc1-b826-00e9af7e74d6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_ed090980-153f-47f4-9c61-48a44204d7dc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_424cd41d-ff4a-4cc1-b826-00e9af7e74d6" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_ed090980-153f-47f4-9c61-48a44204d7dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentAdvisoryAgreementMember_e679c5e6-3ce9-4ef9-a289-d62a3b6791a3" xlink:href="fsk-20250331.xsd#fsk_InvestmentAdvisoryAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_ed090980-153f-47f4-9c61-48a44204d7dc" xlink:to="loc_fsk_InvestmentAdvisoryAgreementMember_e679c5e6-3ce9-4ef9-a289-d62a3b6791a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_be0654e1-e283-404f-ba55-eff16690bde7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ba17b9f3-da5a-445c-8398-9a500146b1d6" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_be0654e1-e283-404f-ba55-eff16690bde7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_be0654e1-e283-404f-ba55-eff16690bde7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_be0654e1-e283-404f-ba55-eff16690bde7" xlink:to="loc_us-gaap_RelatedPartyDomain_be0654e1-e283-404f-ba55-eff16690bde7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_0e9c1a07-a612-44de-85f6-26776aa416f7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_be0654e1-e283-404f-ba55-eff16690bde7" xlink:to="loc_us-gaap_RelatedPartyDomain_0e9c1a07-a612-44de-85f6-26776aa416f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AffiliatedEntityMember_36239618-2bdb-4fd4-b31d-45d0d17c8562" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_AffiliatedEntityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_0e9c1a07-a612-44de-85f6-26776aa416f7" xlink:to="loc_srt_AffiliatedEntityMember_36239618-2bdb-4fd4-b31d-45d0d17c8562" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_c7765901-5e01-499a-84cb-d7abca5460de" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ba17b9f3-da5a-445c-8398-9a500146b1d6" xlink:to="loc_us-gaap_CreditFacilityAxis_c7765901-5e01-499a-84cb-d7abca5460de" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_c7765901-5e01-499a-84cb-d7abca5460de_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_c7765901-5e01-499a-84cb-d7abca5460de" xlink:to="loc_us-gaap_CreditFacilityDomain_c7765901-5e01-499a-84cb-d7abca5460de_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_8cc08788-b0bc-4682-899e-ad19fc63eb83" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_c7765901-5e01-499a-84cb-d7abca5460de" xlink:to="loc_us-gaap_CreditFacilityDomain_8cc08788-b0bc-4682-899e-ad19fc63eb83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_d1e4bafa-305e-4898-ab28-40ded5e1875f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_8cc08788-b0bc-4682-899e-ad19fc63eb83" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_d1e4bafa-305e-4898-ab28-40ded5e1875f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_770cf612-ca73-4b07-a7fc-682b8d246e53" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ba17b9f3-da5a-445c-8398-9a500146b1d6" xlink:to="loc_us-gaap_DebtInstrumentAxis_770cf612-ca73-4b07-a7fc-682b8d246e53" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_770cf612-ca73-4b07-a7fc-682b8d246e53_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_770cf612-ca73-4b07-a7fc-682b8d246e53" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_770cf612-ca73-4b07-a7fc-682b8d246e53_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_68711096-3d4f-45a8-ade8-6f39a13343ae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_770cf612-ca73-4b07-a7fc-682b8d246e53" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_68711096-3d4f-45a8-ade8-6f39a13343ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_MeadowbrookRunCreditFacilityMember_eaab297c-e7e0-469e-8a7c-cab417fc51f8" xlink:href="fsk-20250331.xsd#fsk_MeadowbrookRunCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_68711096-3d4f-45a8-ade8-6f39a13343ae" xlink:to="loc_fsk_MeadowbrookRunCreditFacilityMember_eaab297c-e7e0-469e-8a7c-cab417fc51f8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SeniorSecuredRevolvingCreditFacilityMember_2d60c29c-d141-4dfd-bae4-e07a7ce9dc03" xlink:href="fsk-20250331.xsd#fsk_SeniorSecuredRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_68711096-3d4f-45a8-ade8-6f39a13343ae" xlink:to="loc_fsk_SeniorSecuredRevolvingCreditFacilityMember_2d60c29c-d141-4dfd-bae4-e07a7ce9dc03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ClassA1SeniorSecuredFloatingRateNotesMember_fc9a76cd-1937-44f7-b774-d19f5662ccee" xlink:href="fsk-20250331.xsd#fsk_ClassA1SeniorSecuredFloatingRateNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_68711096-3d4f-45a8-ade8-6f39a13343ae" xlink:to="loc_fsk_ClassA1SeniorSecuredFloatingRateNotesMember_fc9a76cd-1937-44f7-b774-d19f5662ccee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ClassA1LSeniorSecuredFloatingRateLoansMember_e26fd328-96c3-4333-9e26-a51a70ce3d0d" xlink:href="fsk-20250331.xsd#fsk_ClassA1LSeniorSecuredFloatingRateLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_68711096-3d4f-45a8-ade8-6f39a13343ae" xlink:to="loc_fsk_ClassA1LSeniorSecuredFloatingRateLoansMember_e26fd328-96c3-4333-9e26-a51a70ce3d0d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ClassA1WSeniorSecuredFloatingRateLoansMember_304507cc-3e50-47d1-8149-68fefdcb338c" xlink:href="fsk-20250331.xsd#fsk_ClassA1WSeniorSecuredFloatingRateLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_68711096-3d4f-45a8-ade8-6f39a13343ae" xlink:to="loc_fsk_ClassA1WSeniorSecuredFloatingRateLoansMember_304507cc-3e50-47d1-8149-68fefdcb338c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ClassA2SeniorSecuredFloatingRateNotesMember_6d80df2c-3034-477c-bd43-49a265375d0f" xlink:href="fsk-20250331.xsd#fsk_ClassA2SeniorSecuredFloatingRateNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_68711096-3d4f-45a8-ade8-6f39a13343ae" xlink:to="loc_fsk_ClassA2SeniorSecuredFloatingRateNotesMember_6d80df2c-3034-477c-bd43-49a265375d0f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ClassA2LSeniorSecuredFloatingRateLoansMember_9bf40140-5355-42cb-91c0-083e5e4faf7f" xlink:href="fsk-20250331.xsd#fsk_ClassA2LSeniorSecuredFloatingRateLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_68711096-3d4f-45a8-ade8-6f39a13343ae" xlink:to="loc_fsk_ClassA2LSeniorSecuredFloatingRateLoansMember_9bf40140-5355-42cb-91c0-083e5e4faf7f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ClassBSeniorSecuredFloatingRateNotesMember_264b6979-5004-49d8-ad4e-cf9f2106f53b" xlink:href="fsk-20250331.xsd#fsk_ClassBSeniorSecuredFloatingRateNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_68711096-3d4f-45a8-ade8-6f39a13343ae" xlink:to="loc_fsk_ClassBSeniorSecuredFloatingRateNotesMember_264b6979-5004-49d8-ad4e-cf9f2106f53b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ClassCSecuredDeferrableFloatingRateNotesMember_0f387294-2e97-44f8-8435-cc991ebe1564" xlink:href="fsk-20250331.xsd#fsk_ClassCSecuredDeferrableFloatingRateNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_68711096-3d4f-45a8-ade8-6f39a13343ae" xlink:to="loc_fsk_ClassCSecuredDeferrableFloatingRateNotesMember_0f387294-2e97-44f8-8435-cc991ebe1564" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A8625UnsecuredNotesDue2025Member_07876325-8db7-4aa4-89d4-bca259dc5db2" xlink:href="fsk-20250331.xsd#fsk_A8625UnsecuredNotesDue2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_68711096-3d4f-45a8-ade8-6f39a13343ae" xlink:to="loc_fsk_A8625UnsecuredNotesDue2025Member_07876325-8db7-4aa4-89d4-bca259dc5db2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_48a23353-803b-445c-9259-c9c2cd7eb98d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ba17b9f3-da5a-445c-8398-9a500146b1d6" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_48a23353-803b-445c-9259-c9c2cd7eb98d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_48a23353-803b-445c-9259-c9c2cd7eb98d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_48a23353-803b-445c-9259-c9c2cd7eb98d" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_48a23353-803b-445c-9259-c9c2cd7eb98d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_98b20a44-ace7-4931-8870-40e5cd79e23f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_48a23353-803b-445c-9259-c9c2cd7eb98d" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_98b20a44-ace7-4931-8870-40e5cd79e23f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_95fe6872-df8e-4a21-9b16-1bb9a4e79362" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_98b20a44-ace7-4931-8870-40e5cd79e23f" xlink:to="loc_us-gaap_LineOfCreditMember_95fe6872-df8e-4a21-9b16-1bb9a4e79362" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_eadd365c-3a2c-462a-80d2-63fcc903a8cd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_98b20a44-ace7-4931-8870-40e5cd79e23f" xlink:to="loc_us-gaap_SeniorNotesMember_eadd365c-3a2c-462a-80d2-63fcc903a8cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_9096bceb-4a0b-4401-a95d-25a3da4a20bd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_98b20a44-ace7-4931-8870-40e5cd79e23f" xlink:to="loc_us-gaap_UnsecuredDebtMember_9096bceb-4a0b-4401-a95d-25a3da4a20bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanySeniorSecurityIndebtednessAssetCoverageRatio_82ce1810-bf2e-4d11-bb4d-c62e2986716f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanySeniorSecurityIndebtednessAssetCoverageRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:to="loc_us-gaap_InvestmentCompanySeniorSecurityIndebtednessAssetCoverageRatio_82ce1810-bf2e-4d11-bb4d-c62e2986716f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_b40274fc-d4cd-4d39-9675-352b09902ad5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_b40274fc-d4cd-4d39-9675-352b09902ad5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAverageAmountOutstanding_25157b76-810d-48c2-9006-306771fe5365" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtAverageAmountOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:to="loc_us-gaap_LongTermDebtAverageAmountOutstanding_25157b76-810d-48c2-9006-306771fe5365" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtWeightedAverageInterestRate_d8755ec4-6c9b-4642-8d2a-82ecf925f15b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtWeightedAverageInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:to="loc_us-gaap_DebtWeightedAverageInterestRate_d8755ec4-6c9b-4642-8d2a-82ecf925f15b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_bf136b11-017f-4505-adb9-a52da8ada985" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_bf136b11-017f-4505-adb9-a52da8ada985" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_6c16932f-8c7c-4b77-9a1b-5072fd7b57e5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_6c16932f-8c7c-4b77-9a1b-5072fd7b57e5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_DebtInstrumentBasisSpreadOnVariableRateAmortizationPeriod_0be0c1f1-911c-42eb-937c-7455b7637d6c" xlink:href="fsk-20250331.xsd#fsk_DebtInstrumentBasisSpreadOnVariableRateAmortizationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:to="loc_fsk_DebtInstrumentBasisSpreadOnVariableRateAmortizationPeriod_0be0c1f1-911c-42eb-937c-7455b7637d6c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_fe1056ae-0b0a-4bc3-bc34-44353009e6d3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_fe1056ae-0b0a-4bc3-bc34-44353009e6d3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_7291a196-7a10-46e9-83c7-c2593ec89ae1" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:to="loc_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_7291a196-7a10-46e9-83c7-c2593ec89ae1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedBalancePrincipalAmount_cbe55ce1-835d-4963-b988-a60425b06518" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedBalancePrincipalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:to="loc_us-gaap_InvestmentOwnedBalancePrincipalAmount_cbe55ce1-835d-4963-b988-a60425b06518" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentBasisSpreadVariableRate_1538c9a6-67d6-426b-a6b7-3ca5e77c1ef7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentBasisSpreadVariableRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:to="loc_us-gaap_InvestmentBasisSpreadVariableRate_1538c9a6-67d6-426b-a6b7-3ca5e77c1ef7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentOwnedUnderlyingFaceAmountAtMarketValue_819cab68-d535-40f5-bfce-737ae2eb53a8" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentOwnedUnderlyingFaceAmountAtMarketValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:to="loc_us-gaap_InvestmentOwnedUnderlyingFaceAmountAtMarketValue_819cab68-d535-40f5-bfce-737ae2eb53a8" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_81101c47-d1a2-4dd5-af14-e4045447e65c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_391034d9-d616-4d65-bf65-19df586f70d0" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_81101c47-d1a2-4dd5-af14-e4045447e65c" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/FinancingArrangementsScheduleofOutstandingFinancingArrangementsDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#FinancingArrangementsScheduleofOutstandingFinancingArrangementsDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/FinancingArrangementsScheduleofOutstandingFinancingArrangementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_73ed071e-6feb-418f-9727-91e6e2efcc3d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:to="loc_us-gaap_DebtInstrumentTable_73ed071e-6feb-418f-9727-91e6e2efcc3d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_2ee380ef-c336-4b2b-b861-e069f3790919" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_73ed071e-6feb-418f-9727-91e6e2efcc3d" xlink:to="loc_us-gaap_CreditFacilityAxis_2ee380ef-c336-4b2b-b861-e069f3790919" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_2ee380ef-c336-4b2b-b861-e069f3790919_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_2ee380ef-c336-4b2b-b861-e069f3790919" xlink:to="loc_us-gaap_CreditFacilityDomain_2ee380ef-c336-4b2b-b861-e069f3790919_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_80157165-2f7f-4d45-9720-a8f97f248cbc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_2ee380ef-c336-4b2b-b861-e069f3790919" xlink:to="loc_us-gaap_CreditFacilityDomain_80157165-2f7f-4d45-9720-a8f97f248cbc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_92d00f13-a0bc-4477-9439-3673c4a65f1a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_80157165-2f7f-4d45-9720-a8f97f248cbc" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_92d00f13-a0bc-4477-9439-3673c4a65f1a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StandbyLettersOfCreditMember_8cbeff24-f11a-4717-b944-401e6e161ea6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StandbyLettersOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_80157165-2f7f-4d45-9720-a8f97f248cbc" xlink:to="loc_us-gaap_StandbyLettersOfCreditMember_8cbeff24-f11a-4717-b944-401e6e161ea6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_51ee8c8b-bfe3-4adb-b34f-43874cf2542a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_73ed071e-6feb-418f-9727-91e6e2efcc3d" xlink:to="loc_us-gaap_DebtInstrumentAxis_51ee8c8b-bfe3-4adb-b34f-43874cf2542a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_51ee8c8b-bfe3-4adb-b34f-43874cf2542a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_51ee8c8b-bfe3-4adb-b34f-43874cf2542a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_51ee8c8b-bfe3-4adb-b34f-43874cf2542a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_51ee8c8b-bfe3-4adb-b34f-43874cf2542a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AmblerCreditFacilityMember_85ffde19-c4ce-4dec-9ee9-4412e7817b14" xlink:href="fsk-20250331.xsd#fsk_AmblerCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_AmblerCreditFacilityMember_85ffde19-c4ce-4dec-9ee9-4412e7817b14" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CCTTokyoFundingCreditFacilityMember_309a3207-360d-470c-904a-81ee35a60380" xlink:href="fsk-20250331.xsd#fsk_CCTTokyoFundingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_CCTTokyoFundingCreditFacilityMember_309a3207-360d-470c-904a-81ee35a60380" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_DarbyCreekCreditFacilityMember_2e8fa926-f34a-4f74-8f51-20e528147a81" xlink:href="fsk-20250331.xsd#fsk_DarbyCreekCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_DarbyCreekCreditFacilityMember_2e8fa926-f34a-4f74-8f51-20e528147a81" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_MeadowbrookRunCreditFacilityMember_e115e704-37a3-4827-9d89-245f8e2866d9" xlink:href="fsk-20250331.xsd#fsk_MeadowbrookRunCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_MeadowbrookRunCreditFacilityMember_e115e704-37a3-4827-9d89-245f8e2866d9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SeniorSecuredRevolvingCreditFacilityMember_e23e248c-36c6-485f-9a25-a7dde4ac5fb5" xlink:href="fsk-20250331.xsd#fsk_SeniorSecuredRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_SeniorSecuredRevolvingCreditFacilityMember_e23e248c-36c6-485f-9a25-a7dde4ac5fb5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A4125UnsecuredNotesDue2025Member_d3daed66-87a4-45ac-a6e8-0e2590c105b8" xlink:href="fsk-20250331.xsd#fsk_A4125UnsecuredNotesDue2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A4125UnsecuredNotesDue2025Member_d3daed66-87a4-45ac-a6e8-0e2590c105b8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A4250UnsecuredNotesDue2025Member_26c34824-83d8-4b70-a655-4c9163f0645a" xlink:href="fsk-20250331.xsd#fsk_A4250UnsecuredNotesDue2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A4250UnsecuredNotesDue2025Member_26c34824-83d8-4b70-a655-4c9163f0645a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A8625UnsecuredNotesDue2025Member_3d09367b-969d-42bd-afe4-bef3f53aa592" xlink:href="fsk-20250331.xsd#fsk_A8625UnsecuredNotesDue2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A8625UnsecuredNotesDue2025Member_3d09367b-969d-42bd-afe4-bef3f53aa592" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A3400UnsecuredNotesDue2026Member_fd5f4f6d-1972-4df6-9198-22981d0d8151" xlink:href="fsk-20250331.xsd#fsk_A3400UnsecuredNotesDue2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A3400UnsecuredNotesDue2026Member_fd5f4f6d-1972-4df6-9198-22981d0d8151" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A2625UnsecuredNotesDue2027Member_40f20fe1-da84-4f1b-8fb7-2588d648c3ae" xlink:href="fsk-20250331.xsd#fsk_A2625UnsecuredNotesDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A2625UnsecuredNotesDue2027Member_40f20fe1-da84-4f1b-8fb7-2588d648c3ae" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A3250UnsecuredNotesDue2027Member_b6ef8748-9cb3-406a-9ad2-e0ddaeb9465d" xlink:href="fsk-20250331.xsd#fsk_A3250UnsecuredNotesDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A3250UnsecuredNotesDue2027Member_b6ef8748-9cb3-406a-9ad2-e0ddaeb9465d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A3125UnsecuredNotesDue2028Member_e1ebc549-2af5-4aca-8882-2eaea41278b5" xlink:href="fsk-20250331.xsd#fsk_A3125UnsecuredNotesDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A3125UnsecuredNotesDue2028Member_e1ebc549-2af5-4aca-8882-2eaea41278b5" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A7875UnsecuredNotesDue2029Member_1fb5541c-dbf3-4ee4-893c-bbd29144f382" xlink:href="fsk-20250331.xsd#fsk_A7875UnsecuredNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A7875UnsecuredNotesDue2029Member_1fb5541c-dbf3-4ee4-893c-bbd29144f382" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A6.875UnsecuredNotesDue2029Member_f0e912e4-9a9d-472d-81c7-f63ec2d78cf3" xlink:href="fsk-20250331.xsd#fsk_A6.875UnsecuredNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A6.875UnsecuredNotesDue2029Member_f0e912e4-9a9d-472d-81c7-f63ec2d78cf3" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A6.125UnsecuredNotesDue2030Member_c2c6bbd3-e64b-4f44-8041-f247e8bc7b05" xlink:href="fsk-20250331.xsd#fsk_A6.125UnsecuredNotesDue2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A6.125UnsecuredNotesDue2030Member_c2c6bbd3-e64b-4f44-8041-f247e8bc7b05" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CollateralizedLoanObligationUnsecuredNotesMember_0128538f-fd3e-4a3b-b3b2-c5db5574800d" xlink:href="fsk-20250331.xsd#fsk_CollateralizedLoanObligationUnsecuredNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_CollateralizedLoanObligationUnsecuredNotesMember_0128538f-fd3e-4a3b-b3b2-c5db5574800d" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CollateralizedLoanObligationUnsecuredNotesOneMember_4a9f4d9e-b0be-478d-b47f-e486f46783f9" xlink:href="fsk-20250331.xsd#fsk_CollateralizedLoanObligationUnsecuredNotesOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_CollateralizedLoanObligationUnsecuredNotesOneMember_4a9f4d9e-b0be-478d-b47f-e486f46783f9" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A190TermLoanOutstandingMember_2da1ba32-5a94-4092-a7bf-e35e497652f3" xlink:href="fsk-20250331.xsd#fsk_A190TermLoanOutstandingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A190TermLoanOutstandingMember_2da1ba32-5a94-4092-a7bf-e35e497652f3" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A205CommitmentsOutstandingMember_ad3c6d2b-d73b-404d-8b95-15939db0b0b0" xlink:href="fsk-20250331.xsd#fsk_A205CommitmentsOutstandingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A205CommitmentsOutstandingMember_ad3c6d2b-d73b-404d-8b95-15939db0b0b0" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A185ClassA1RNotesOutstandingMember_92c636af-f411-47a9-92b5-b27a2f91e45c" xlink:href="fsk-20250331.xsd#fsk_A185ClassA1RNotesOutstandingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A185ClassA1RNotesOutstandingMember_92c636af-f411-47a9-92b5-b27a2f91e45c" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A225ClassA2RNotesOutstandingMember_dc6c03c0-4116-4f85-8153-5d4044dc27f8" xlink:href="fsk-20250331.xsd#fsk_A225ClassA2RNotesOutstandingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A225ClassA2RNotesOutstandingMember_dc6c03c0-4116-4f85-8153-5d4044dc27f8" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A260ClassB1RNotesOutstandingMember_c7db766b-dc65-4840-af12-da319aeb1414" xlink:href="fsk-20250331.xsd#fsk_A260ClassB1RNotesOutstandingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A260ClassB1RNotesOutstandingMember_c7db766b-dc65-4840-af12-da319aeb1414" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A3011ClassB2RNotesOutstandingMember_8ccae5e2-d570-4db1-bba5-712b6217d5ba" xlink:href="fsk-20250331.xsd#fsk_A3011ClassB2RNotesOutstandingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A3011ClassB2RNotesOutstandingMember_8ccae5e2-d570-4db1-bba5-712b6217d5ba" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A1.48ClassA1NotesOutstandingMember_be3ff9e6-7928-4456-87f0-c45c3e1c942d" xlink:href="fsk-20250331.xsd#fsk_A1.48ClassA1NotesOutstandingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A1.48ClassA1NotesOutstandingMember_be3ff9e6-7928-4456-87f0-c45c3e1c942d" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A1.48ClassA1LNotesOutstandingMember_124bfbfd-35e2-438a-a9f0-f29397b20e6a" xlink:href="fsk-20250331.xsd#fsk_A1.48ClassA1LNotesOutstandingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A1.48ClassA1LNotesOutstandingMember_124bfbfd-35e2-438a-a9f0-f29397b20e6a" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A1.48ClassA1WNotesOutstandingMember_23648783-c90b-4f03-b673-78c8027576a4" xlink:href="fsk-20250331.xsd#fsk_A1.48ClassA1WNotesOutstandingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A1.48ClassA1WNotesOutstandingMember_23648783-c90b-4f03-b673-78c8027576a4" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A1.60ClassA2LNotesOutstandingMember_b2ca50e2-f532-4247-862d-a32f8bf96934" xlink:href="fsk-20250331.xsd#fsk_A1.60ClassA2LNotesOutstandingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_A1.60ClassA2LNotesOutstandingMember_b2ca50e2-f532-4247-862d-a32f8bf96934" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ClassBNotesOutstandingMember_8fc31b47-7463-4dfd-9e34-f0dde66eae5c" xlink:href="fsk-20250331.xsd#fsk_ClassBNotesOutstandingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_ClassBNotesOutstandingMember_8fc31b47-7463-4dfd-9e34-f0dde66eae5c" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_ClassCNotesOutstandingMember_08bdf85d-bea9-4dab-bf70-738a1cdae9a5" xlink:href="fsk-20250331.xsd#fsk_ClassCNotesOutstandingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_ClassCNotesOutstandingMember_08bdf85d-bea9-4dab-bf70-738a1cdae9a5" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_BurholmePrimeBrokerageFacilityMember_c0e0fd97-5ec9-4d0c-8805-c8e7940300cc" xlink:href="fsk-20250331.xsd#fsk_BurholmePrimeBrokerageFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_ae1aedc4-5aad-4ad4-a370-103152f3f725" xlink:to="loc_fsk_BurholmePrimeBrokerageFacilityMember_c0e0fd97-5ec9-4d0c-8805-c8e7940300cc" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_5a454195-9409-4322-bc8c-5e758623ab12" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_73ed071e-6feb-418f-9727-91e6e2efcc3d" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_5a454195-9409-4322-bc8c-5e758623ab12" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_5a454195-9409-4322-bc8c-5e758623ab12_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_5a454195-9409-4322-bc8c-5e758623ab12" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_5a454195-9409-4322-bc8c-5e758623ab12_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_10bdf424-0186-4ccc-a52b-2ac532c493c7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_5a454195-9409-4322-bc8c-5e758623ab12" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_10bdf424-0186-4ccc-a52b-2ac532c493c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_2a49349f-b019-4afa-8cf2-1e56302af948" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_10bdf424-0186-4ccc-a52b-2ac532c493c7" xlink:to="loc_us-gaap_LineOfCreditMember_2a49349f-b019-4afa-8cf2-1e56302af948" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_1271bb1b-9bde-4587-bb37-a05b65a9782f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_10bdf424-0186-4ccc-a52b-2ac532c493c7" xlink:to="loc_us-gaap_UnsecuredDebtMember_1271bb1b-9bde-4587-bb37-a05b65a9782f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralizedLoanObligationsMember_cb5e831c-435c-4dbb-b63a-2c7927ef0320" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CollateralizedLoanObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_10bdf424-0186-4ccc-a52b-2ac532c493c7" xlink:to="loc_us-gaap_CollateralizedLoanObligationsMember_cb5e831c-435c-4dbb-b63a-2c7927ef0320" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_1b234d5b-e538-43ea-b65b-f90a3b0c2d8d" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_73ed071e-6feb-418f-9727-91e6e2efcc3d" xlink:to="loc_srt_RangeAxis_1b234d5b-e538-43ea-b65b-f90a3b0c2d8d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1b234d5b-e538-43ea-b65b-f90a3b0c2d8d_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_1b234d5b-e538-43ea-b65b-f90a3b0c2d8d" xlink:to="loc_srt_RangeMember_1b234d5b-e538-43ea-b65b-f90a3b0c2d8d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_fefd98e6-d45e-4c4f-bea9-2e35330787ee" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_1b234d5b-e538-43ea-b65b-f90a3b0c2d8d" xlink:to="loc_srt_RangeMember_fefd98e6-d45e-4c4f-bea9-2e35330787ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_5f67cf6c-bd1a-497f-b2eb-34c5e70c78e3" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_fefd98e6-d45e-4c4f-bea9-2e35330787ee" xlink:to="loc_srt_MaximumMember_5f67cf6c-bd1a-497f-b2eb-34c5e70c78e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_0f782501-abe1-487f-9962-95c3e9fe2157" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_fefd98e6-d45e-4c4f-bea9-2e35330787ee" xlink:to="loc_srt_MinimumMember_0f782501-abe1-487f-9962-95c3e9fe2157" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CurrencyAxis_9bc7775a-af26-4749-b664-05110858dd4d" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CurrencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_73ed071e-6feb-418f-9727-91e6e2efcc3d" xlink:to="loc_srt_CurrencyAxis_9bc7775a-af26-4749-b664-05110858dd4d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_9bc7775a-af26-4749-b664-05110858dd4d_default" xlink:href="https://xbrl.sec.gov/currency/2024/currency-2024.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CurrencyAxis_9bc7775a-af26-4749-b664-05110858dd4d" xlink:to="loc_currency_AllCurrenciesDomain_9bc7775a-af26-4749-b664-05110858dd4d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AllCurrenciesDomain_f3073792-45b0-42c4-83e9-033b87820fb1" xlink:href="https://xbrl.sec.gov/currency/2024/currency-2024.xsd#currency_AllCurrenciesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CurrencyAxis_9bc7775a-af26-4749-b664-05110858dd4d" xlink:to="loc_currency_AllCurrenciesDomain_f3073792-45b0-42c4-83e9-033b87820fb1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_USD_f1dc93a7-5f44-4c17-a264-a2a509ca9b2b" xlink:href="https://xbrl.sec.gov/currency/2024/currency-2024.xsd#currency_USD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_f3073792-45b0-42c4-83e9-033b87820fb1" xlink:to="loc_currency_USD_f1dc93a7-5f44-4c17-a264-a2a509ca9b2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_GBP_d8103711-e387-49f5-bff4-41a6d6502299" xlink:href="https://xbrl.sec.gov/currency/2024/currency-2024.xsd#currency_GBP"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_f3073792-45b0-42c4-83e9-033b87820fb1" xlink:to="loc_currency_GBP_d8103711-e387-49f5-bff4-41a6d6502299" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_EUR_71f003f2-b1d4-4b63-94e6-093996ca4267" xlink:href="https://xbrl.sec.gov/currency/2024/currency-2024.xsd#currency_EUR"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_f3073792-45b0-42c4-83e9-033b87820fb1" xlink:to="loc_currency_EUR_71f003f2-b1d4-4b63-94e6-093996ca4267" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_AUD_f73ce6a3-7071-4f2f-b861-f62927794404" xlink:href="https://xbrl.sec.gov/currency/2024/currency-2024.xsd#currency_AUD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_f3073792-45b0-42c4-83e9-033b87820fb1" xlink:to="loc_currency_AUD_f73ce6a3-7071-4f2f-b861-f62927794404" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_currency_CAD_9dd7c437-3270-490c-af5e-e82ad0ca9f74" xlink:href="https://xbrl.sec.gov/currency/2024/currency-2024.xsd#currency_CAD"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_currency_AllCurrenciesDomain_f3073792-45b0-42c4-83e9-033b87820fb1" xlink:to="loc_currency_CAD_9dd7c437-3270-490c-af5e-e82ad0ca9f74" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_d3533473-4533-4ea1-9675-40ded12fb17f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_73ed071e-6feb-418f-9727-91e6e2efcc3d" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_d3533473-4533-4ea1-9675-40ded12fb17f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_d3533473-4533-4ea1-9675-40ded12fb17f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_d3533473-4533-4ea1-9675-40ded12fb17f" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_d3533473-4533-4ea1-9675-40ded12fb17f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_9c41138e-3651-4c39-9bcb-99ba8e253f73" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_d3533473-4533-4ea1-9675-40ded12fb17f" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_9c41138e-3651-4c39-9bcb-99ba8e253f73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_e4e99bd6-d48d-42b8-a7d0-693bf936d37d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_9c41138e-3651-4c39-9bcb-99ba8e253f73" xlink:to="loc_us-gaap_InterestRateSwapMember_e4e99bd6-d48d-42b8-a7d0-693bf936d37d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_6eb2d6bc-17ab-4b82-86a5-d3bba66898cd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_6eb2d6bc-17ab-4b82-86a5-d3bba66898cd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_5c4b0d6d-3402-4eb6-b2b4-69ef846c937e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_5c4b0d6d-3402-4eb6-b2b4-69ef846c937e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_0f026831-1245-41bf-811a-d3e7184bffe9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_0f026831-1245-41bf-811a-d3e7184bffe9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_aaf38521-a2f3-4d0c-a7e9-1457c9da4037" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_aaf38521-a2f3-4d0c-a7e9-1457c9da4037" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_DebtInstrumentVariableRateFloor_393bcd02-5b73-4f03-8bf7-7027f7d81e3a" xlink:href="fsk-20250331.xsd#fsk_DebtInstrumentVariableRateFloor"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:to="loc_fsk_DebtInstrumentVariableRateFloor_393bcd02-5b73-4f03-8bf7-7027f7d81e3a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_TermLoanOutstanding_0a5ddc27-5769-4583-8ff8-939199a035a4" xlink:href="fsk-20250331.xsd#fsk_TermLoanOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:to="loc_fsk_TermLoanOutstanding_0a5ddc27-5769-4583-8ff8-939199a035a4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_RevolvingCommitmentOutstanding_7279cb88-f78a-48cf-99e7-0ff5493928e2" xlink:href="fsk-20250331.xsd#fsk_RevolvingCommitmentOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:to="loc_fsk_RevolvingCommitmentOutstanding_7279cb88-f78a-48cf-99e7-0ff5493928e2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_DebtInstrumentBasisSpreadOnVariableRateCreditSpreadAdjustment_b7645c8e-95e3-4056-8611-15928853e2f7" xlink:href="fsk-20250331.xsd#fsk_DebtInstrumentBasisSpreadOnVariableRateCreditSpreadAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:to="loc_fsk_DebtInstrumentBasisSpreadOnVariableRateCreditSpreadAdjustment_b7645c8e-95e3-4056-8611-15928853e2f7" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyExchangeRateTranslation1_f6153ad4-9953-4839-9540-bb80da0194fd" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ForeignCurrencyExchangeRateTranslation1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:to="loc_us-gaap_ForeignCurrencyExchangeRateTranslation1_f6153ad4-9953-4839-9540-bb80da0194fd" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_f1bbcde2-1a0a-416f-97b2-0523e7453128" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:to="loc_us-gaap_LineOfCredit_f1bbcde2-1a0a-416f-97b2-0523e7453128" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_9567704e-feca-44ef-be83-9fc01f3c7e33" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:to="loc_us-gaap_LongTermDebtFairValue_9567704e-feca-44ef-be83-9fc01f3c7e33" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_ce1f23ca-5cda-46bb-9e9e-dead09cf9197" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DerivativeFairValueOfDerivativeAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:to="loc_us-gaap_DerivativeFairValueOfDerivativeAsset_ce1f23ca-5cda-46bb-9e9e-dead09cf9197" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_DebtInstrumentCreditSpreadAdjustment_396b4585-62ab-4311-b7e7-db66c052f8c5" xlink:href="fsk-20250331.xsd#fsk_DebtInstrumentCreditSpreadAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_de99360b-e952-4a44-9543-0b69fef0f51e" xlink:to="loc_fsk_DebtInstrumentCreditSpreadAdjustment_396b4585-62ab-4311-b7e7-db66c052f8c5" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/FinancingArrangementsScheduleofInterestExpenseDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#FinancingArrangementsScheduleofInterestExpenseDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/FinancingArrangementsScheduleofInterestExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtLineItems_25fdf4c6-b6f6-4d81-a00c-0f90c2f270ae" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ShortTermDebtLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShortTermDebtTable_dc846cc4-f6d8-4e03-b122-f42242222e32" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ScheduleOfShortTermDebtTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShortTermDebtLineItems_25fdf4c6-b6f6-4d81-a00c-0f90c2f270ae" xlink:to="loc_us-gaap_ScheduleOfShortTermDebtTable_dc846cc4-f6d8-4e03-b122-f42242222e32" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_3fe8eb42-2fb4-49a2-8786-6836117efcf9" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShortTermDebtTable_dc846cc4-f6d8-4e03-b122-f42242222e32" xlink:to="loc_us-gaap_CreditFacilityAxis_3fe8eb42-2fb4-49a2-8786-6836117efcf9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_3fe8eb42-2fb4-49a2-8786-6836117efcf9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_3fe8eb42-2fb4-49a2-8786-6836117efcf9" xlink:to="loc_us-gaap_CreditFacilityDomain_3fe8eb42-2fb4-49a2-8786-6836117efcf9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_5165895f-7a4b-48e4-9c66-91a43bed1573" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_3fe8eb42-2fb4-49a2-8786-6836117efcf9" xlink:to="loc_us-gaap_CreditFacilityDomain_5165895f-7a4b-48e4-9c66-91a43bed1573" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_e6aa32f3-4ae7-4cf4-ba15-488ac4f7157b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_5165895f-7a4b-48e4-9c66-91a43bed1573" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_e6aa32f3-4ae7-4cf4-ba15-488ac4f7157b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_ee2645a5-17eb-4e79-9ceb-b4cfbf51a010" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShortTermDebtTable_dc846cc4-f6d8-4e03-b122-f42242222e32" xlink:to="loc_us-gaap_DebtInstrumentAxis_ee2645a5-17eb-4e79-9ceb-b4cfbf51a010" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_ee2645a5-17eb-4e79-9ceb-b4cfbf51a010_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_ee2645a5-17eb-4e79-9ceb-b4cfbf51a010" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_ee2645a5-17eb-4e79-9ceb-b4cfbf51a010_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_ee2645a5-17eb-4e79-9ceb-b4cfbf51a010" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_AmblerCreditFacilityMember_5206028e-5ea0-4493-bf6a-c455c6c6c3b1" xlink:href="fsk-20250331.xsd#fsk_AmblerCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_AmblerCreditFacilityMember_5206028e-5ea0-4493-bf6a-c455c6c6c3b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CCTTokyoFundingCreditFacilityMember_c4a54cc8-645c-45ef-8fe6-c949b0bc90b3" xlink:href="fsk-20250331.xsd#fsk_CCTTokyoFundingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_CCTTokyoFundingCreditFacilityMember_c4a54cc8-645c-45ef-8fe6-c949b0bc90b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_DarbyCreekCreditFacilityMember_d10c0cfe-7780-4154-8080-3405a2f6bb0a" xlink:href="fsk-20250331.xsd#fsk_DarbyCreekCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_DarbyCreekCreditFacilityMember_d10c0cfe-7780-4154-8080-3405a2f6bb0a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_MeadowbrookRunCreditFacilityMember_8cc3936d-d12f-4185-ae77-c134cbefb4f6" xlink:href="fsk-20250331.xsd#fsk_MeadowbrookRunCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_MeadowbrookRunCreditFacilityMember_8cc3936d-d12f-4185-ae77-c134cbefb4f6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SeniorSecuredRevolvingCreditFacilityMember_d1e9b7f4-3d14-4163-870c-270ee237ed75" xlink:href="fsk-20250331.xsd#fsk_SeniorSecuredRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_SeniorSecuredRevolvingCreditFacilityMember_d1e9b7f4-3d14-4163-870c-270ee237ed75" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A4625UnsecuredNotesDue2024Member_f0d5b079-0de3-4b4a-bfa7-d01ff22c5bb1" xlink:href="fsk-20250331.xsd#fsk_A4625UnsecuredNotesDue2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_A4625UnsecuredNotesDue2024Member_f0d5b079-0de3-4b4a-bfa7-d01ff22c5bb1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A1650UnsecuredNotesDue2024Member_c065fa23-5177-446f-9e32-74f58deb063b" xlink:href="fsk-20250331.xsd#fsk_A1650UnsecuredNotesDue2024Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_A1650UnsecuredNotesDue2024Member_c065fa23-5177-446f-9e32-74f58deb063b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A4125UnsecuredNotesDue2025Member_9f4d36db-513c-4a26-9d33-544ec3e845a9" xlink:href="fsk-20250331.xsd#fsk_A4125UnsecuredNotesDue2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_A4125UnsecuredNotesDue2025Member_9f4d36db-513c-4a26-9d33-544ec3e845a9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A4250UnsecuredNotesDue2025Member_6a626cbd-f45a-45b7-beed-94a02dc2e863" xlink:href="fsk-20250331.xsd#fsk_A4250UnsecuredNotesDue2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_A4250UnsecuredNotesDue2025Member_6a626cbd-f45a-45b7-beed-94a02dc2e863" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A8625UnsecuredNotesDue2025Member_e53e4ffc-8905-488d-96fe-65175435203e" xlink:href="fsk-20250331.xsd#fsk_A8625UnsecuredNotesDue2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_A8625UnsecuredNotesDue2025Member_e53e4ffc-8905-488d-96fe-65175435203e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A3400UnsecuredNotesDue2026Member_f8bfb5c8-942a-4be8-893c-6ec2e04ff141" xlink:href="fsk-20250331.xsd#fsk_A3400UnsecuredNotesDue2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_A3400UnsecuredNotesDue2026Member_f8bfb5c8-942a-4be8-893c-6ec2e04ff141" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A2625UnsecuredNotesDue2027Member_9c54ec4a-172d-4722-9f83-7f779fd05dc9" xlink:href="fsk-20250331.xsd#fsk_A2625UnsecuredNotesDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_A2625UnsecuredNotesDue2027Member_9c54ec4a-172d-4722-9f83-7f779fd05dc9" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A3250UnsecuredNotesDue2027Member_ecdb66ff-aa1c-4e43-a3f3-0750e81dd3a8" xlink:href="fsk-20250331.xsd#fsk_A3250UnsecuredNotesDue2027Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_A3250UnsecuredNotesDue2027Member_ecdb66ff-aa1c-4e43-a3f3-0750e81dd3a8" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A3125UnsecuredNotesDue2028Member_025ad694-d285-4fa2-af45-bd237429654d" xlink:href="fsk-20250331.xsd#fsk_A3125UnsecuredNotesDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_A3125UnsecuredNotesDue2028Member_025ad694-d285-4fa2-af45-bd237429654d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A7875UnsecuredNotesDue2029Member_c1e004cc-298f-47c4-8646-5c935c5d0081" xlink:href="fsk-20250331.xsd#fsk_A7875UnsecuredNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_A7875UnsecuredNotesDue2029Member_c1e004cc-298f-47c4-8646-5c935c5d0081" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A6.875UnsecuredNotesDue2029Member_a08e193e-d40b-469f-92ab-64079b040117" xlink:href="fsk-20250331.xsd#fsk_A6.875UnsecuredNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_A6.875UnsecuredNotesDue2029Member_a08e193e-d40b-469f-92ab-64079b040117" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_A6.125UnsecuredNotesDue2030Member_50bdd27b-c5f1-4ba3-bb02-8be6750f4584" xlink:href="fsk-20250331.xsd#fsk_A6.125UnsecuredNotesDue2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_A6.125UnsecuredNotesDue2030Member_50bdd27b-c5f1-4ba3-bb02-8be6750f4584" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CollateralizedLoanObligationUnsecuredNotesMember_a866251b-eeca-4195-8e5d-adba8cc581ec" xlink:href="fsk-20250331.xsd#fsk_CollateralizedLoanObligationUnsecuredNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_CollateralizedLoanObligationUnsecuredNotesMember_a866251b-eeca-4195-8e5d-adba8cc581ec" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CollateralizedLoanObligationUnsecuredNotesOneMember_c1a27240-15db-4ca9-8d64-885deb51e251" xlink:href="fsk-20250331.xsd#fsk_CollateralizedLoanObligationUnsecuredNotesOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_da1ffd66-b193-40be-9aab-09dbd7e0c971" xlink:to="loc_fsk_CollateralizedLoanObligationUnsecuredNotesOneMember_c1a27240-15db-4ca9-8d64-885deb51e251" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_004de225-6c6c-474c-8c18-66fb5ca45877" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShortTermDebtTable_dc846cc4-f6d8-4e03-b122-f42242222e32" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_004de225-6c6c-474c-8c18-66fb5ca45877" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_004de225-6c6c-474c-8c18-66fb5ca45877_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_004de225-6c6c-474c-8c18-66fb5ca45877" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_004de225-6c6c-474c-8c18-66fb5ca45877_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_ade8c815-9f1c-4f51-ba81-a7c8b5ade8e0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_004de225-6c6c-474c-8c18-66fb5ca45877" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_ade8c815-9f1c-4f51-ba81-a7c8b5ade8e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_eedfa4ac-273c-487f-b542-a910ae2d584d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_ade8c815-9f1c-4f51-ba81-a7c8b5ade8e0" xlink:to="loc_us-gaap_LineOfCreditMember_eedfa4ac-273c-487f-b542-a910ae2d584d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_367cd15e-44e2-4562-b9c7-7c79298bd8e5" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_ade8c815-9f1c-4f51-ba81-a7c8b5ade8e0" xlink:to="loc_us-gaap_UnsecuredDebtMember_367cd15e-44e2-4562-b9c7-7c79298bd8e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_209b6ac6-7a7e-452b-92cc-5f8238164f21" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtLineItems_25fdf4c6-b6f6-4d81-a00c-0f90c2f270ae" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_209b6ac6-7a7e-452b-92cc-5f8238164f21" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebtExcludingAmortization_5e7892d7-4d81-44fe-ac1e-da48bb3af470" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpenseDebtExcludingAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtLineItems_25fdf4c6-b6f6-4d81-a00c-0f90c2f270ae" xlink:to="loc_us-gaap_InterestExpenseDebtExcludingAmortization_5e7892d7-4d81-44fe-ac1e-da48bb3af470" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfDebtDiscountPremium_349fdfed-326b-418b-83de-bf741346d07c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_AmortizationOfDebtDiscountPremium"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtLineItems_25fdf4c6-b6f6-4d81-a00c-0f90c2f270ae" xlink:to="loc_us-gaap_AmortizationOfDebtDiscountPremium_349fdfed-326b-418b-83de-bf741346d07c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_97b58109-d394-4ed5-bd24-c9fb42240068" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtLineItems_25fdf4c6-b6f6-4d81-a00c-0f90c2f270ae" xlink:to="loc_us-gaap_InterestExpenseDebt_97b58109-d394-4ed5-bd24-c9fb42240068" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/CommitmentsandContingenciesScheduleofUnfundedCommitmentsDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#CommitmentsandContingenciesScheduleofUnfundedCommitmentsDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/CommitmentsandContingenciesScheduleofUnfundedCommitmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportForNonconsolidatedLegalEntityLineItems_5537961f-f03a-4ab2-a552-480b66eb8ac0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportForNonconsolidatedLegalEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportForNonconsolidatedLegalEntityTable_ff4f24f7-44fb-4d2c-ab07-aabb8f8ba940" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportForNonconsolidatedLegalEntityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancialSupportForNonconsolidatedLegalEntityLineItems_5537961f-f03a-4ab2-a552-480b66eb8ac0" xlink:to="loc_us-gaap_FinancialSupportForNonconsolidatedLegalEntityTable_ff4f24f7-44fb-4d2c-ab07-aabb8f8ba940" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIdentifierAxis_e0995c36-e87d-445b-9114-a7098bfefc88" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentIdentifierAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FinancialSupportForNonconsolidatedLegalEntityTable_ff4f24f7-44fb-4d2c-ab07-aabb8f8ba940" xlink:to="loc_us-gaap_InvestmentIdentifierAxis_e0995c36-e87d-445b-9114-a7098bfefc88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_504474ec-b492-4e8f-b12f-036437f4fb30" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FinancialSupportForNonconsolidatedLegalEntityTable_ff4f24f7-44fb-4d2c-ab07-aabb8f8ba940" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_504474ec-b492-4e8f-b12f-036437f4fb30" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_504474ec-b492-4e8f-b12f-036437f4fb30_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_504474ec-b492-4e8f-b12f-036437f4fb30" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_504474ec-b492-4e8f-b12f-036437f4fb30_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_0c8fff21-27aa-4519-b7d2-8e1d3a873968" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_504474ec-b492-4e8f-b12f-036437f4fb30" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_0c8fff21-27aa-4519-b7d2-8e1d3a873968" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_UnfundedDebtSecuritiesMember_f06f34a5-63d3-4eb2-8d4f-336201b2ccb6" xlink:href="fsk-20250331.xsd#fsk_UnfundedDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_0c8fff21-27aa-4519-b7d2-8e1d3a873968" xlink:to="loc_fsk_UnfundedDebtSecuritiesMember_f06f34a5-63d3-4eb2-8d4f-336201b2ccb6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_UnfundedEquityOtherCommitmentsMember_83b7d05c-1b25-441f-87e0-cbc3140c85e6" xlink:href="fsk-20250331.xsd#fsk_UnfundedEquityOtherCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_0c8fff21-27aa-4519-b7d2-8e1d3a873968" xlink:to="loc_fsk_UnfundedEquityOtherCommitmentsMember_83b7d05c-1b25-441f-87e0-cbc3140c85e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyFinancialCommitmentToInvesteeFutureAmount_12d4579b-267c-4168-9ce6-96345394a9ed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyFinancialCommitmentToInvesteeFutureAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportForNonconsolidatedLegalEntityLineItems_5537961f-f03a-4ab2-a552-480b66eb8ac0" xlink:to="loc_us-gaap_InvestmentCompanyFinancialCommitmentToInvesteeFutureAmount_12d4579b-267c-4168-9ce6-96345394a9ed" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/CommitmentsandContingenciesScheduleofUnfundedCommitmentsDetails_1" xlink:type="simple" xlink:href="fsk-20250331.xsd#CommitmentsandContingenciesScheduleofUnfundedCommitmentsDetails_1"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/CommitmentsandContingenciesScheduleofUnfundedCommitmentsDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportForNonconsolidatedLegalEntityLineItems_5537961f-f03a-4ab2-a552-480b66eb8ac0" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportForNonconsolidatedLegalEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportForNonconsolidatedLegalEntityTable_ff4f24f7-44fb-4d2c-ab07-aabb8f8ba940" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportForNonconsolidatedLegalEntityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancialSupportForNonconsolidatedLegalEntityLineItems_5537961f-f03a-4ab2-a552-480b66eb8ac0" xlink:to="loc_us-gaap_FinancialSupportForNonconsolidatedLegalEntityTable_ff4f24f7-44fb-4d2c-ab07-aabb8f8ba940" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_504474ec-b492-4e8f-b12f-036437f4fb30" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FinancialSupportForNonconsolidatedLegalEntityTable_ff4f24f7-44fb-4d2c-ab07-aabb8f8ba940" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_504474ec-b492-4e8f-b12f-036437f4fb30" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_504474ec-b492-4e8f-b12f-036437f4fb30_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_504474ec-b492-4e8f-b12f-036437f4fb30" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_504474ec-b492-4e8f-b12f-036437f4fb30_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_0c8fff21-27aa-4519-b7d2-8e1d3a873968" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_504474ec-b492-4e8f-b12f-036437f4fb30" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_0c8fff21-27aa-4519-b7d2-8e1d3a873968" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_UnfundedDebtSecuritiesMember_f06f34a5-63d3-4eb2-8d4f-336201b2ccb6" xlink:href="fsk-20250331.xsd#fsk_UnfundedDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_0c8fff21-27aa-4519-b7d2-8e1d3a873968" xlink:to="loc_fsk_UnfundedDebtSecuritiesMember_f06f34a5-63d3-4eb2-8d4f-336201b2ccb6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_UnfundedEquityOtherCommitmentsMember_83b7d05c-1b25-441f-87e0-cbc3140c85e6" xlink:href="fsk-20250331.xsd#fsk_UnfundedEquityOtherCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_0c8fff21-27aa-4519-b7d2-8e1d3a873968" xlink:to="loc_fsk_UnfundedEquityOtherCommitmentsMember_83b7d05c-1b25-441f-87e0-cbc3140c85e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyFinancialCommitmentToInvesteeFutureAmount_12d4579b-267c-4168-9ce6-96345394a9ed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyFinancialCommitmentToInvesteeFutureAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportForNonconsolidatedLegalEntityLineItems_5537961f-f03a-4ab2-a552-480b66eb8ac0" xlink:to="loc_us-gaap_InvestmentCompanyFinancialCommitmentToInvesteeFutureAmount_12d4579b-267c-4168-9ce6-96345394a9ed" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#CommitmentsandContingenciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsLineItems_a84f1c8d-0fbc-4e4d-84b8-fd41e865db8e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherCommitmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsTable_d20137c5-f223-4422-9c33-a229026d128b" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_OtherCommitmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_a84f1c8d-0fbc-4e4d-84b8-fd41e865db8e" xlink:to="loc_us-gaap_OtherCommitmentsTable_d20137c5-f223-4422-9c33-a229026d128b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_551cec29-08cc-482e-9927-db9976aec1bc" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_d20137c5-f223-4422-9c33-a229026d128b" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_551cec29-08cc-482e-9927-db9976aec1bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_551cec29-08cc-482e-9927-db9976aec1bc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_551cec29-08cc-482e-9927-db9976aec1bc" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_551cec29-08cc-482e-9927-db9976aec1bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_8adc26a8-5072-4baa-b2ae-590ebb54541d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityAxis_551cec29-08cc-482e-9927-db9976aec1bc" xlink:to="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_8adc26a8-5072-4baa-b2ae-590ebb54541d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_DebtSecuritiesRevolvingCreditFacilityMember_1436be31-cebc-4d2b-bf18-b613de621adc" xlink:href="fsk-20250331.xsd#fsk_DebtSecuritiesRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_8adc26a8-5072-4baa-b2ae-590ebb54541d" xlink:to="loc_fsk_DebtSecuritiesRevolvingCreditFacilityMember_1436be31-cebc-4d2b-bf18-b613de621adc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DelayedDrawTermLoanMember_7d86d454-5bef-41fc-8278-66812b4d6c6a" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DelayedDrawTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_8adc26a8-5072-4baa-b2ae-590ebb54541d" xlink:to="loc_us-gaap_DelayedDrawTermLoanMember_7d86d454-5bef-41fc-8278-66812b4d6c6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesMember_9182d454-d686-4e0d-aeaf-638404a79d39" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_8adc26a8-5072-4baa-b2ae-590ebb54541d" xlink:to="loc_us-gaap_DebtSecuritiesMember_9182d454-d686-4e0d-aeaf-638404a79d39" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_PartnershipInterestMember_65ebb26a-d520-481f-99b1-bda57a0f0e42" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_PartnershipInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialSupportToNonconsolidatedLegalEntityDomain_8adc26a8-5072-4baa-b2ae-590ebb54541d" xlink:to="loc_srt_PartnershipInterestMember_65ebb26a-d520-481f-99b1-bda57a0f0e42" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_ddd087d3-28bf-4b03-9769-056429291172" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_d20137c5-f223-4422-9c33-a229026d128b" xlink:to="loc_us-gaap_CreditFacilityAxis_ddd087d3-28bf-4b03-9769-056429291172" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_ddd087d3-28bf-4b03-9769-056429291172_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_ddd087d3-28bf-4b03-9769-056429291172" xlink:to="loc_us-gaap_CreditFacilityDomain_ddd087d3-28bf-4b03-9769-056429291172_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_50b85bcb-d28f-4ec9-b1b5-f0024854de1f" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_ddd087d3-28bf-4b03-9769-056429291172" xlink:to="loc_us-gaap_CreditFacilityDomain_50b85bcb-d28f-4ec9-b1b5-f0024854de1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_5460a01f-0b9f-46e7-ba78-20aee839c5d7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_50b85bcb-d28f-4ec9-b1b5-f0024854de1f" xlink:to="loc_us-gaap_LetterOfCreditMember_5460a01f-0b9f-46e7-ba78-20aee839c5d7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_b2622c8b-8365-4c12-a10a-fd82f3584989" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_d20137c5-f223-4422-9c33-a229026d128b" xlink:to="loc_us-gaap_DebtInstrumentAxis_b2622c8b-8365-4c12-a10a-fd82f3584989" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_b2622c8b-8365-4c12-a10a-fd82f3584989_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_b2622c8b-8365-4c12-a10a-fd82f3584989" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_b2622c8b-8365-4c12-a10a-fd82f3584989_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_b73769d0-76f4-4001-bf03-77d4c30c7c06" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_b2622c8b-8365-4c12-a10a-fd82f3584989" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_b73769d0-76f4-4001-bf03-77d4c30c7c06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_SeniorSecuredRevolvingCreditFacilityMember_1ec7dc54-792c-40d1-9765-6d636f584295" xlink:href="fsk-20250331.xsd#fsk_SeniorSecuredRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_b73769d0-76f4-4001-bf03-77d4c30c7c06" xlink:to="loc_fsk_SeniorSecuredRevolvingCreditFacilityMember_1ec7dc54-792c-40d1-9765-6d636f584295" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_b3789a2a-cc00-4d54-a8b6-305c37b61ee6" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_d20137c5-f223-4422-9c33-a229026d128b" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_b3789a2a-cc00-4d54-a8b6-305c37b61ee6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_b3789a2a-cc00-4d54-a8b6-305c37b61ee6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_b3789a2a-cc00-4d54-a8b6-305c37b61ee6" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_b3789a2a-cc00-4d54-a8b6-305c37b61ee6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_0ac7a167-8ac9-4532-9c68-5e41186d6798" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_b3789a2a-cc00-4d54-a8b6-305c37b61ee6" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_0ac7a167-8ac9-4532-9c68-5e41186d6798" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_3af05103-4f82-4c83-a14a-4ee88be913a3" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_0ac7a167-8ac9-4532-9c68-5e41186d6798" xlink:to="loc_us-gaap_LineOfCreditMember_3af05103-4f82-4c83-a14a-4ee88be913a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_136ae7d6-16cd-4a5f-b4ab-84098bc7cbd4" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_d20137c5-f223-4422-9c33-a229026d128b" xlink:to="loc_srt_CounterpartyNameAxis_136ae7d6-16cd-4a5f-b4ab-84098bc7cbd4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_136ae7d6-16cd-4a5f-b4ab-84098bc7cbd4_default" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_136ae7d6-16cd-4a5f-b4ab-84098bc7cbd4" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_136ae7d6-16cd-4a5f-b4ab-84098bc7cbd4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_6100ce18-c72b-46c7-bb91-eb4cfb6d0f27" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_136ae7d6-16cd-4a5f-b4ab-84098bc7cbd4" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_6100ce18-c72b-46c7-bb91-eb4cfb6d0f27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_2a5d3a03-a6d7-49c8-bb90-b9e5f40b4227" xlink:href="fsk-20250331.xsd#fsk_CreditOpportunitiesPartnersJVLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_6100ce18-c72b-46c7-bb91-eb4cfb6d0f27" xlink:to="loc_fsk_CreditOpportunitiesPartnersJVLLCMember_2a5d3a03-a6d7-49c8-bb90-b9e5f40b4227" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_161cd3b2-839d-429f-a305-3a2439f6818c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_d20137c5-f223-4422-9c33-a229026d128b" xlink:to="loc_us-gaap_InvestmentTypeAxis_161cd3b2-839d-429f-a305-3a2439f6818c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_161cd3b2-839d-429f-a305-3a2439f6818c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_161cd3b2-839d-429f-a305-3a2439f6818c" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_161cd3b2-839d-429f-a305-3a2439f6818c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_0dfd7256-e46d-4351-857c-e2e30de3dc49" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_161cd3b2-839d-429f-a305-3a2439f6818c" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_0dfd7256-e46d-4351-857c-e2e30de3dc49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_PartnershipInterestMember_2b760512-406a-4bb1-9c30-2059a4c84e92" xlink:href="https://xbrl.fasb.org/srt/2024/elts/srt-2024.xsd#srt_PartnershipInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_0dfd7256-e46d-4351-857c-e2e30de3dc49" xlink:to="loc_srt_PartnershipInterestMember_2b760512-406a-4bb1-9c30-2059a4c84e92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentCompanyFinancialCommitmentToInvesteeFutureAmount_75d47cc6-bc6c-46ac-8667-b9bcbd6e0586" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_InvestmentCompanyFinancialCommitmentToInvesteeFutureAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_a84f1c8d-0fbc-4e4d-84b8-fd41e865db8e" xlink:to="loc_us-gaap_InvestmentCompanyFinancialCommitmentToInvesteeFutureAmount_75d47cc6-bc6c-46ac-8667-b9bcbd6e0586" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_InvestmentCompanyFinancialCommitmentToInvesteeUnrealizedAppreciationDepreciation_5b83951e-ff1a-4061-b342-4583f35e2bea" xlink:href="fsk-20250331.xsd#fsk_InvestmentCompanyFinancialCommitmentToInvesteeUnrealizedAppreciationDepreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_a84f1c8d-0fbc-4e4d-84b8-fd41e865db8e" xlink:to="loc_fsk_InvestmentCompanyFinancialCommitmentToInvesteeUnrealizedAppreciationDepreciation_5b83951e-ff1a-4061-b342-4583f35e2bea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_c1b53e31-a06b-482e-abc1-19822a4af4ca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_a84f1c8d-0fbc-4e4d-84b8-fd41e865db8e" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_c1b53e31-a06b-482e-abc1-19822a4af4ca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_6bbb9907-cacd-4c33-b10c-b74bb3444145" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_a84f1c8d-0fbc-4e4d-84b8-fd41e865db8e" xlink:to="loc_us-gaap_LineOfCredit_6bbb9907-cacd-4c33-b10c-b74bb3444145" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fskkrcapitalcorp.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="fsk-20250331.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://fskkrcapitalcorp.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_4ef43ed4-9eb4-441c-b050-44418508762c" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_75070414-4603-4d23-bcb0-f99126f6cacb" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_4ef43ed4-9eb4-441c-b050-44418508762c" xlink:to="loc_us-gaap_SubsequentEventTable_75070414-4603-4d23-bcb0-f99126f6cacb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_bd4404c5-da75-43df-ab45-a046218b8db7" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_75070414-4603-4d23-bcb0-f99126f6cacb" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_bd4404c5-da75-43df-ab45-a046218b8db7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_bd4404c5-da75-43df-ab45-a046218b8db7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_bd4404c5-da75-43df-ab45-a046218b8db7" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_bd4404c5-da75-43df-ab45-a046218b8db7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_e15fe10e-b811-46a4-9c96-6a76ca884d4e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_bd4404c5-da75-43df-ab45-a046218b8db7" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_e15fe10e-b811-46a4-9c96-6a76ca884d4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_b69bdfb9-f13a-4752-b09e-0de02a7601ed" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_e15fe10e-b811-46a4-9c96-6a76ca884d4e" xlink:to="loc_us-gaap_SubsequentEventMember_b69bdfb9-f13a-4752-b09e-0de02a7601ed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsAxis_03a2ccb3-1f7e-47f3-92a1-af0d67f0355d" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_75070414-4603-4d23-bcb0-f99126f6cacb" xlink:to="loc_us-gaap_DividendsAxis_03a2ccb3-1f7e-47f3-92a1-af0d67f0355d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_03a2ccb3-1f7e-47f3-92a1-af0d67f0355d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DividendsAxis_03a2ccb3-1f7e-47f3-92a1-af0d67f0355d" xlink:to="loc_us-gaap_DividendsDomain_03a2ccb3-1f7e-47f3-92a1-af0d67f0355d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_37754f26-b0fc-4c00-bf96-3d82c2b27955" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DividendsAxis_03a2ccb3-1f7e-47f3-92a1-af0d67f0355d" xlink:to="loc_us-gaap_DividendsDomain_37754f26-b0fc-4c00-bf96-3d82c2b27955" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_O2025Q2RegularDividendsMember_c82523cd-efbc-4c19-9e94-23885122950a" xlink:href="fsk-20250331.xsd#fsk_O2025Q2RegularDividendsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DividendsDomain_37754f26-b0fc-4c00-bf96-3d82c2b27955" xlink:to="loc_fsk_O2025Q2RegularDividendsMember_c82523cd-efbc-4c19-9e94-23885122950a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_fsk_O2025Q2SupplementalDividendsMember_240552fe-bd1d-47bd-aeef-63f5895cac5c" xlink:href="fsk-20250331.xsd#fsk_O2025Q2SupplementalDividendsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DividendsDomain_37754f26-b0fc-4c00-bf96-3d82c2b27955" xlink:to="loc_fsk_O2025Q2SupplementalDividendsMember_240552fe-bd1d-47bd-aeef-63f5895cac5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_9ac7b113-c00a-4628-9b70-98078861bd10" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_4ef43ed4-9eb4-441c-b050-44418508762c" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_9ac7b113-c00a-4628-9b70-98078861bd10" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
