Counter or resist (6)
I believe the answer is:
oppose
I believe this is a double definition.
'counter' is the first definition.
(I've seen this before)
'resist' is the second definition.
(I've seen this before)
(Other definitions for oppose that I've seen before include "'Refute, stand against (6)'" , "Act against" , "Bar" , "Counter" , "Obstruct, resist" .)