More hideous (6)
I believe the answer is:
uglier
'more hideous' is the definition.
('ugly' can be similar in meaning to 'hideous')
This is all the clue.
(Other definitions for uglier that I've seen before include "More hideous" , "More displeasing to the senses" , "Less beautiful" , "More unpleasant to look at" , "More unsightly" .)