Seasonal wind (7)
I believe the answer is:
monsoon
'seasonal wind' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for monsoon that I've seen before include "Seasonal wind (south-west or north-east) of southern Asia" , "Rain-bringing weather feature" , "Asian wind; rainy season" , "Seasonal wind or rainy season in S Asia" , "Rainy season in southern Asia" .)