Interpol argument concealed, opposed (5)
I believe the answer is:
polar
'opposed' is the definition.
(thesaurus)
'interpol argument concealed' is the wordplay.
'concealed' indicates the answer is hidden within the clue.
'POLAR' is hidden in the letters of 'interpol argument'.
(Other definitions for polar that I've seen before include "Kind of bear or opposite" , "Relating to the highest latitudes" , "Relating to the end regions of the earth's axis" , "Type of bear" , "-- Bear; -- circle" .)