More unattractive (6)
I believe the answer is:
uglier
'more unattractive' is the definition.
('ugly' is associated in meaning with 'unattractive')
This is all the clue.
(Other definitions for uglier that I've seen before include "More unattractive or repellent to the eye" , "More deficient in beauty" , "More hideous" , "Less appealing" , "Less beautiful" .)