Contend with an opinion (4)
I believe the answer is:
view
'an opinion' is the definition.
('view' can be a synonym of 'opinion')
'contend with' is the wordplay.
'contend' becomes 'vie' (synonyms).
'with' becomes 'w' (abbreviation).
'vie'+'w'='VIEW'
(Other definitions for view that I've seen before include "Natural scenery or mental attitude" , "Judge" , "Range or field of vision" , "See" , "'Aspect, panorama (4)'" .)