Disputing remark on profit (10)
I believe the answer is:
'disputing' is the definition.
('gainsay' can be a synonym of 'dispute')
'remark on profit' is the wordplay.
'remark' becomes 'saying' (I can't explain this - if you can you should believe this answer much more).
'on' is a charade indicator (letters next to each other).
'profit' becomes 'gain' (synonyms).
'saying' after 'gain' is 'GAINSAYING'.
Can you help me to learn more?
(Other definitions for gainsaying that I've seen before include "Not agreeing" , "denial" .)