One fat round Scottish landowner (5)
I believe the answer is:
laird
'scottish landowner' is the definition.
(I've seen this in another clue)
'one fat round' is the wordplay.
'one' becomes 'i' (Roman numeral).
'fat' becomes 'lard' (lard is a kind of fat).
'round' indicates putting letters inside.
'i' placed into 'lard' is 'LAIRD'.
(Other definitions for laird that I've seen before include "Scots estate owner" , "One's landed in Scotland" , "Scottish landowner" , "Scottish squire" , "Scottish estate-owner" .)