demesne vs seigneury

demesne and seigneury both are nouns.

Word	Noun	Adjective	Verb	Adverb
demesne	Yes	No	No	No
seigneury	Yes	No	No	No

As nouns, seigneury is a hyponym of demesne; that is, seigneury is a word with a more specific, narrower meaning than demesne:

demesne: extensive landed property (especially in the country) retained by the owner for his own use
seigneury: the estate of a seigneur

demesne (noun)	seigneury (noun)
territory over which rule or control is exercised	the position and authority of a feudal lord
extensive landed property (especially in the country) retained by the owner for his own use	the estate of a seigneur