Unusually frosty north: undergarment found (1-6)
I believe the answer is:
y-fronts
'undergarment found' is the definition.
(Y-fronts are a type of undergarment)
'unusually frosty north' is the wordplay.
'unusually' indicates an anagram.
'north' becomes 'N' (synonyms).
'frosty'+'n'='frostyn'
'frostyn' is an anagram of 'Y-FRONTS'.
(Other definitions for y-fronts that I've seen before include "Men's pants" , "Item of male clothing" , "Men's underpants" , "Pants for men" , "Men's underwear" .)