Company man is convincing (6)
I believe the answer is:
cogent
'is convincing' is the definition.
(similar in meaning)
'company man' is the wordplay.
'company' becomes 'co' (abbreviation).
'man' becomes 'gent' (gent is a kind of man).
'co'+'gent'='COGENT'
(Other definitions for cogent that I've seen before include "Well argued, compelling" , "Clearly argued" , "Forcefully convincing" , "Clear, logical and convincing" , "Convincingly argued" .)