Opposes (7)
I believe the answer is:
resists
'opposes' is the definition.
(resisting is a kind of opposing)
This is the entire clue.
(Other definitions for resists that I've seen before include "Opposes, puts up fight" , "Stands up to, withstands" , "Tries to stop" , "Sisters (anag.)" , "Is hostile to" .)