Deficit reduced some months before winter (9)
I believe the answer is:
shortfall
'deficit' is the definition.
(I know that deficit can be written as shortfall)
'reduced some months before winter' is the wordplay.
'reduced' becomes 'short' (shortened).
'some months before winter' becomes 'fall' (fall can mean autumn).
'short'+'fall'='SHORTFALL'
(Other definitions for shortfall that I've seen before include "lack" , "Deficiency" , "Loss" , "what we're lacking" , "Not enough money" .)