Sordid gain could be cruel (5)
I believe the answer is:
lucre
'sordid gain' is the definition.
(I've seen this before)
'could be cruel' is the wordplay.
'could be' indicates anagramming the letters.
'cruel' anagrammed gives 'LUCRE'.
(Other definitions for lucre that I've seen before include "ill-gotten gain" , "benefits from crime" , "monetary gain" , "Sordid gain; riches" , "Cruel kind of money, may be filthy" .)