Terribly evil and disgusting (4)
I believe the answer is:
vile
'disgusting' is the definition.
(I've seen this in another clue)
'terribly evil' is the wordplay.
'terribly' indicates anagramming the letters.
'evil' anagrammed gives 'VILE'.
'and' acts as a link.
(Other definitions for vile that I've seen before include "Terrible" , "Despicable in evil way" , "Evil - evil (anag)" , "Loathsome - draw veil over it" , "Noxious" .)