Fat, heartless Scottish landowner (4)
I believe the answer is:
lard
'fat' is the definition.
(I know that lard is a type of edible fats and oils)
'heartless scottish landowner' is the wordplay.
'heartless' suggests removing the centre.
'scottish landowner' becomes 'laird' (I've seen this before).
'laird' with its centre removed is 'LARD'.
(Other definitions for lard that I've seen before include "Fat Scottish landowner appears disheartened" , "F [FAT]" , "Animal fat" , "Clarified pig fat" , "Pig-fat" .)