Less dirty (7)
I believe the answer is:
cleaner
'less dirty' is the definition.
('clean' can be the opposite of 'dirty' so perhaps 'cleaner' is reasonable for 'less dirty')
This is the entire clue.
(Other definitions for cleaner that I've seen before include "Char; detergent" , "Less soiled" , "More hygienic" , "One who dusts or vacuums" , "Chemical agent for removing dirt" .)