Small difference of opinion remains (5)
I believe the answer is:
stiff
'remains' is the definition.
(synonyms)
'small difference of opinion' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'difference of opinion' becomes 'tiff' (tiff is a kind of difference of opinion).
's'+'tiff'='STIFF'
(Other definitions for stiff that I've seen before include "Formal" , "Not giving" , "Rigid, prim" , "Unfriendly" , "Severe - conventional - dead body" .)