Sordid gain could give you ulcer (5)
I believe the answer is:
lucre
'sordid gain' is the definition.
(I've seen this before)
'could give you ulcer' is the wordplay.
'could give you' indicates an anagram (the same letters can give another word).
'ulcer' is an anagram of 'LUCRE'.
(Other definitions for lucre that I've seen before include "(Dishonourably gained) money (poetic, literary)" , "Archaic wealth, may be filthy" , "Cash" , "financial gain" , "There's money" .)