Illicit payment (8)
I believe the answer is:
kickback
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">illicit payment</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for kickback that I've seen before include "Recoil; illicit payment" , "strong reaction" , "Underhand payment" , "(Illicit) confidential payment to facilitator" , "Bribe - recoil" .)