Left atmosphere at home (4)
I believe the answer is:
lair
'home' is the definition.
(I know that lair is a type of home)
'left atmosphere' is the wordplay.
'left' becomes 'l' (common abbreviation).
'atmosphere' becomes 'air' (synonyms).
'l'+'air'='LAIR'
'at' acts as a link.
(Other definitions for lair that I've seen before include "Wild animal's place of refuge" , "Place of seclusion (informal)" , "Supposed large ape, the Bigfoot" , "secluded spot?" , "Waylay" .)