Attitude after line in retreat (4)
I believe the answer is:
lair
'retreat' is the definition.
(both can mean a private hideout)
'attitude after line' is the wordplay.
'attitude' becomes 'air' (I've seen this before).
'after' says to put letters next to each other.
'line' becomes 'l' (used when specifying particular lines from a poem).
'air' after 'l' is 'LAIR'.
'in' is the link.
(Other definitions for lair that I've seen before include "Place to hide" , "secluded spot?" , "Waylay" , "A nautical hail" , "Burrow" .)