Left atmosphere in burrow (4)
I believe the answer is:
lair
'burrow' is the definition.
(thesaurus)
'left atmosphere' is the wordplay.
'left' becomes 'l' (common abbreviation).
'atmosphere' becomes 'air' ('air' can be a synonym of 'atmosphere').
'l'+'air'='LAIR'
'in' is the link.
(Other definitions for lair that I've seen before include "Study" , "Den of a wild animal" , "mire where he lives" , "beastly retreat" , "Place to hide" .)