Gain made by professional in good condition (6)
I believe the answer is:
profit
'gain' is the definition.
(synonyms)
'by professional in good condition' is the wordplay.
'by' means one lot of letters go next to another.
'professional' becomes 'pro' (abbreviation).
'in good condition' becomes 'fit' (I've seen this in another clue).
'pro' put next to 'fit' is 'PROFIT'.
'made' acts as a link.
(Other definitions for profit that I've seen before include "financial advantage" , "Gain, return on investment" , "Financial gain" , "returns" , "Net gain after expenses" .)