Forcible business man (6)
I believe the answer is:
cogent
'forcible' is the definition.
(I've seen this in another clue)
'business man' is the wordplay.
'business' becomes 'co' (short for company).
'man' becomes 'gent' (gent is a kind of man).
'co'+'gent'='COGENT'
(Other definitions for cogent that I've seen before include "'Powerfully persuasive, argument say (6)'" , "'Clear and logical, argument say (6)'" , "Well-reasoned" , "Convincing, persuasive" , "Convincingly argued" .)