Horrible sweet, is it? (9)
I believe the answer is:
unsavoury
I believe this clue is a double definition.
'horrible' is the first definition.
(both can mean unpleasant)
'sweet is it?' is the second definition.
(in food, sweet is the opposite of savoury)
(Other definitions for unsavoury that I've seen before include "Disreputable" , "Distasteful" , "Nasty - tasteless" , "offensive" , "revolting?" .)