Sordid gain (5)
I believe the answer is:
lucre
'sordid gain' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for lucre that I've seen before include "Ulcer (anag)" , "Possession of the rich" , "Scornful word for money that may be 1 Across" , "(Filthy) profit" , "monetary gain" .)