Withstand, oppose (6)
I believe the answer is:
resist
I believe this is a double definition.
'withstand' is the first definition.
(I know that withstand is a more specific form of the action resist)
'oppose' is the second definition.
(resisting is a kind of opposing)
(Other definitions for resist that I've seen before include "Don't give in" , "turn down" , "Take stand against, oppose" , "Put up fight, oppose forcefully" , "Put up opposition to sister" .)