Arctic fleet (5)
I believe the answer is:
nippy
I believe this is a double definition.
'arctic' is the first definition.
(both can mean cold referring to the weather)
'fleet?' is the second definition.
(both can mean fast)
(Other definitions for nippy that I've seen before include "Frosty - quick" , "like the wind?" , "A bit cold?" , "brisk" , "Very cold - quick (informal)" .)