Forward male beginning to trust a forecaster (7)
I believe the answer is:
prophet
'a forecaster' is the definition.
(I've seen this before)
'forward male beginning to trust' is the wordplay.
'forward' becomes 'prop' (both can mean a type of rugby player).
'male' becomes 'he' (he refers to a man).
'beginning to' says to take the initial letters.
The initial letter of 'trust' is 't'.
'prop'+'he'+'t'='PROPHET'
(Other definitions for prophet that I've seen before include "Tipster possibly" , "Moses, for example" , "Biblical seer" , "One who predicts the future" , "Oracle" .)