Offensive to the senses (4)
I believe the answer is:
foul
'offensive to the senses' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for foul that I've seen before include "Break the rules on the pitch" , "Very unpleasant" , "Abominable - offence on football field" , "Loathsome - tackle breaking game rules" , "Disgusting" .)