Very cold, as a vicious dog might be! (6)
I believe the answer is:
biting
I believe this is a double definition.
'very cold' is the first definition.
'as a vicious dog might be' is the second definition.
(Other definitions for biting that I've seen before include "Keen" , "(Of wit) harsh, cruel" , "Painful or stinging" , "Caustic or cutting - like teeth?" , "Cold - tart" .)