Endlessly chilly in depression (3)
I believe the answer is:
col
'depression' is the definition.
(geographical term for a low point)
'endlessly chilly' is the wordplay.
'endlessly' means to remove the last letter.
'chilly' becomes 'cold' (I've seen this before).
'cold' with its last letter removed is 'COL'.
'in' acts as a link.
(Other definitions for col that I've seen before include "Mountain saddle" , "route through mountains" , "A pass between mountain peaks" , "Mountain defile" , "Depression in range of mountains" .)