Ill-gotten gain
I believe the answer is:
lucre
'ill-gotten gain' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for lucre that I've seen before include "Ill-gotten riches" , "Cruel kind of money, may be filthy" , "Money or wealth" , "Criminal gains maybe" , "(Dishonourably gained) money (poetic, literary)" .)