Forecaster to gain advantage we hear (7)
I believe the answer is:
prophet
'forecaster' is the definition.
(I've seen this before)
'advantage we hear' is the wordplay.
'advantage' becomes 'profit' (profit is a kind of advantage).
'we hear' indicates a 'sounds like' (homophone) clue.
'profit' is a homophone of 'PROPHET'.
'to gain' acts as a link.
(Other definitions for prophet that I've seen before include "Divine spokesman or forecaster" , "Predictor of the future" , "Oracle" , "One who predicts the future" , "Foreteller" .)