Horrible, revolting (6)
I believe the answer is:
grisly
I believe this clue is a double definition.
'horrible' is the first definition.
(I've seen this before)
'revolting' is the second definition.
(thesaurus)
(Other definitions for grisly that I've seen before include "Causing horror or disgust" , "Horrible, ghastly" , "Causing horror or revulsion" , "Horrific" , "Very unpleasant" .)