Disgusting, foul (9)
I believe the answer is:
loathsome
I believe this clue is a double definition.
'disgusting' is the first definition.
(I know that disgusting can be written as loathsome)
'foul' is the second definition.
(I know that foul can be written as loathsome)
(Other definitions for loathsome that I've seen before include "gross" , "15 [ABHORRENT]" , "Disgusting, nauseating" , "Repulsive" , "Hateful" .)