More grubby (7)
I believe the answer is:
dirtier
'more grubby' is the definition.
('dirty' can be similar in meaning to 'grubby')
This is all the clue.
(Other definitions for dirtier that I've seen before include "Less clean" , "More filthy" , "Filthier" , "cleaner? The opposite" , "More grubby" .)