Opposing, contrary (7)
I believe the answer is:
counter
This clue is a double definition.
'opposing' is the first definition.
(I've seen this before)
'contrary' is the second definition.
(I've seen this before)
(Other definitions for counter that I've seen before include "Sales desk" , "Retaliate" , "Small game disc; oppose" , "Piece in board game" , "Table for transactions" .)