I believe the answer is:
'lord's land' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for demesne that I've seen before include "Estate; sound like belittle" , "Extensive landed property" , "Seed men (anag) -- land attached to a property and retained for the owner's personal use" , "Large landed property" , "Seed men on landed estate" .)