Brit's rainwear (3)
I believe the answer is:
mac
'brit's rainwear' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mac that I've seen before include "Waterproof coat (colloq.)" , "Coat - computer" , "Overcoat" , "PC" , "It may help you keep dry" .)