Terribly evil and awful (4)
I believe the answer is:
vile
'awful' is the definition.
(thesaurus)
'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 "Revolting" , "Horrible" , "___ Bodies, Evelyn Waugh's 1930 novel" , "Evil, foul" , "Evil - evil (anag)" .)