Like a bad apple (6)
I believe the answer is:
rotten
'like a bad apple' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rotten that I've seen before include "Falling to pieces from age or morally contemptible" , "Informally, very much" , "Decayed or corrupt (60" , "Decayed or despicable" , "Lousy" .)