It's often filthy and can be cruel (5)
I believe the answer is:
lucre
'it's often filthy' is the definition.
(I've seen this in another clue)
'can be cruel' is the wordplay.
'can be' is an anagram indicator.
'cruel' anagrammed gives 'LUCRE'.
'and' acts as a link.
(Other definitions for lucre that I've seen before include "monetary gain" , "profits" , "Money (especially when gained dishonourably)" , "ill-gotten gains" , "Ill-gotten riches" .)