One entertained by fat Scottish landowner (5)
I believe the answer is:
laird
'scottish landowner' is the definition.
(I've seen this before)
'one entertained by fat' is the wordplay.
'one' becomes 'i' (Roman numeral).
'entertained by' is an insertion indicator (inserted letters are hosted or entertained).
'fat' becomes 'lard' (lard is a kind of fat).
'i' going inside 'lard' is 'LAIRD'.
(Other definitions for laird that I've seen before include "Scottish estate-owner" , "rich Scotsman" , "He's landed in Scotland" , "Scot. landowner" , "Scots landowner" .)