A professional apt to benefit (6)
I believe the answer is:
profit
'to benefit' is the definition.
('profit' can be a synonym of 'benefit')
'a professional apt' is the wordplay.
'a professional' becomes 'pro' (abbreviation).
'apt' becomes 'fit' (I've seen this in another clue).
'pro'+'fit'='PROFIT'
(Other definitions for profit that I've seen before include "Yield - gain" , "financial advantage" , "Surplus earnings" , "Advantage, benefit" , "Money made" .)