I must visit fat Scottish landowner (5)
I believe the answer is:
laird
'scottish landowner' is the definition.
(I've seen this before)
'i must visit fat' is the wordplay.
'must visit' means one lot of letters goes inside another.
'fat' becomes 'lard' (lard is a kind of fat).
'i' placed inside 'lard' is 'LAIRD'.
(Other definitions for laird that I've seen before include "He's landed in Scotland" , "Big landowner" , "Proprietor" , "Scottish squire" , "Man owning land" .)