Forecaster to make gain according to report (7)
I believe the answer is:
prophet
'forecaster' is the definition.
(I've seen this before)
'gain according to report' is the wordplay.
'gain' becomes 'profit' (synonyms).
'according to report' shows a homophone (sound like).
'profit' sounds like 'PROPHET'.
'to make' is the link.
(Other definitions for prophet that I've seen before include "Biblical seer" , "Predictor of the future" , "Religious leader" , "One who anticipates" , "Augur" .)