Scottish landowner’s unfinished retreat (4)
I believe the answer is:
lair
'retreat' is the definition.
(thesaurus)
'scottish landowner's unfinished' is the wordplay.
'scottish landowner' becomes 'laird' (I've seen this before).
'unfinished' means to remove the last letter.
'laird' with its last letter removed is 'LAIR'.
(Other definitions for lair that I've seen before include "secluded spot?" , "Animal's resting place" , "Rail around animal's den" , "Rail about wild animal's home" , "Place to hide" .)