Bad to the bone (4)
I believe the answer is:
evil
'bad to the bone' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for evil that I've seen before include "Morally bad" , "Extremely unpleasant" , "no good in this puzzle" , "Live (anag.)" , "Maleficent" .)