Aesthetically offensive (4)
I believe the answer is:
ugly
'aesthetically offensive' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ugly that I've seen before include "Deficient in beauty" , "Offensive to one's sight or other senses" , "Like an eyesore" , "Of unpleasant appearance" , "Extremely unattractive" .)