Waterproof garment (8)
I believe the answer is:
raincoat
'waterproof garment' is the definition.
(coat worn when it's raining)
This is all the clue.
(Other definitions for raincoat that I've seen before include "which should keep water out" , "Waterproof outer garment" , "Macintosh - with 22a" , "Outer garment for Croatian" , "Wet weather gear" .)