<?xml version="1.0" encoding="utf-8"?>
<!--Generated by DFIN XBRL Instance Document - http://www.dfinsolutions.com/ - Version R3.0 - on 06-April-2024 [03:07:02] {AM}-->
<linkbase xmlns="http://www.xbrl.org/2003/linkbase" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:xbrldt="http://xbrl.org/2005/xbrldt">
<roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2023/ecd-2023.xsd#IndividualsOnly" roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" />
<roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2023/ecd-2023.xsd#PvpAdjustmentsOnly" roleURI="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly" />
<arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" />
<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" />
<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" />
<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" />
<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" />
<arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/notAll" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#notAll" />
<definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly">
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/ecd/2023/ecd-2023.xsd#ecd_AllIndividualsMember" xlink:label="AllIndividualsMember" />
<loc xlink:type="locator" xlink:href="dh-20231231.xsd#dh_MusslewhiteMember" xlink:label="MusslewhiteMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllIndividualsMember" xlink:to="MusslewhiteMember" order="100" />
<loc xlink:type="locator" xlink:href="dh-20231231.xsd#dh_KrantzMember" xlink:label="KrantzMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllIndividualsMember" xlink:to="KrantzMember" order="101" />
<loc xlink:type="locator" xlink:href="dh-20231231.xsd#dh_Messrs.MusslewhiteMember" xlink:label="Messrs.MusslewhiteMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllIndividualsMember" xlink:to="Messrs.MusslewhiteMember" order="102" />
</definitionLink>
<definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly">
<loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/ecd/2023/ecd-2023.xsd#ecd_AllAdjToCompMember" xlink:label="AllAdjToCompMember" />
<loc xlink:type="locator" xlink:href="dh-20231231.xsd#dh_ReportedValueOfEquityAwardsMember" xlink:label="ReportedValueOfEquityAwardsMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="ReportedValueOfEquityAwardsMember" order="103" />
<loc xlink:type="locator" xlink:href="dh-20231231.xsd#dh_EquityAwardAdjustmentsMember" xlink:label="EquityAwardAdjustmentsMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="EquityAwardAdjustmentsMember" order="104" />
<loc xlink:type="locator" xlink:href="dh-20231231.xsd#dh_YearEndFairValueOfEquityAwardsGrantedInTheYearMember" xlink:label="YearEndFairValueOfEquityAwardsGrantedInTheYearMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="YearEndFairValueOfEquityAwardsGrantedInTheYearMember" order="105" />
<loc xlink:type="locator" xlink:href="dh-20231231.xsd#dh_ChangeInFairValueFromEndOfPriorYearToEndOfCoveredYearOfEquityAwardsGrantedInPriorYearsMember" xlink:label="ChangeInFairValueFromEndOfPriorYearToEndOfCoveredYearOfEquityAwardsGrantedInPriorYearsMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="ChangeInFairValueFromEndOfPriorYearToEndOfCoveredYearOfEquityAwardsGrantedInPriorYearsMember" order="106" />
<loc xlink:type="locator" xlink:href="dh-20231231.xsd#dh_ChangeInFairValueOnTheVestingDateOfEquityAwardsGrantedInPriorYearsThatVestedInTheYearMember" xlink:label="ChangeInFairValueOnTheVestingDateOfEquityAwardsGrantedInPriorYearsThatVestedInTheYearMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="ChangeInFairValueOnTheVestingDateOfEquityAwardsGrantedInPriorYearsThatVestedInTheYearMember" order="107" />
<loc xlink:type="locator" xlink:href="dh-20231231.xsd#dh_FairValueAtTheEndOfThePriorYearOfEquityAwardsThatFailedToMeetVestingConditionsInTheYearMember" xlink:label="FairValueAtTheEndOfThePriorYearOfEquityAwardsThatFailedToMeetVestingConditionsInTheYearMember" />
<definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="FairValueAtTheEndOfThePriorYearOfEquityAwardsThatFailedToMeetVestingConditionsInTheYearMember" order="108" />
</definitionLink>
</linkbase>
