Cold, cold mount (5)
I believe the answer is:
chill
'cold' is the definition.
(chill is a kind of cold)
'cold mount' is the wordplay.
'cold' becomes 'c' (eg on taps).
'mount' becomes 'hill' (I've seen this before**).
'c'+'hill'='CHILL'
(Other definitions for chill that I've seen before include "Iciness" , "minor illness" , "Unpleasant coldness in the air" , "Cold feeling" , "nip" .)