What a professional is able to make (6)
I believe the answer is:
profit
'make' is the definition.
(profiting is a kind of making)
'what a professional is able' is the wordplay.
'what a professional' becomes 'pro' (abbreviation).
'is able' becomes 'fit' (similar in meaning).
'pro'+'fit'='PROFIT'
'to' acts as a link.
(Other definitions for profit that I've seen before include "Gain, return on investment" , "Money made" , "Use" , "Yield - gain" , "It's gained on a transaction" .)