Very chilly pass in high surroundings (5-4)
I believe the answer is:
stone-cold
'very chilly' is the definition.
(extremely cold)
'pass in high surroundings' is the wordplay.
'pass in' becomes 'col' (col is a term for a mountain pass. I am not sure about the 'in' bit.).
'high' becomes 'stoned' (on drugs).
'surroundings' is an insertion indicator.
'col' placed into 'stoned' is 'STONE-COLD'.
(Other definitions for stone-cold that I've seen before include "Absolutely without heat" , "Having lost all warmth" , "At a low temperature" .)