Scottish land-owner in retreat before duke (5)
I believe the answer is:
laird
'scottish land-owner' is the definition.
(I've seen this before)
'retreat before duke' is the wordplay.
'retreat' becomes 'lair' (both can mean a private hideout).
'before' means one lot of letters go next to another.
'duke' becomes 'd' (abbreviation).
'lair'+'d'='LAIRD'
'in' acts as a link.
(Other definitions for laird that I've seen before include "Scots landowner" , "Scot. landowner" , "Scottish squire" , "One's landed in Scotland" , "rich Scotsman" .)