Sharp cold (5)
I believe the answer is:
nippy
I believe this clue is a double definition.
'sharp' is the first definition.
(I've seen this before)
'cold' is the second definition.
('nippy' can be similar in meaning to 'cold')
(Other definitions for nippy that I've seen before include "Able to move quickly" , "inclined to bite?" , "Very cold - quick (informal)" , "Nimble; chilly" , "Frosty - quick" .)