dukedom vs demesne

dukedom and demesne both are nouns.

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

As nouns, demesne is a hypernym of dukedom; that is, demesne is a word with a broader meaning than dukedom:

Other hypernyms of dukedom include domain, land.

dukedom (noun)	demesne (noun)
the domain controlled by a duke or duchess	territory over which rule or control is exercised
the dignity or rank or position of a duke	extensive landed property (especially in the country) retained by the owner for his own use