fiefdom vs demesne

fiefdom and demesne both are nouns.

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

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

Other hypernyms of fiefdom include domain, land.

fiefdom (noun)	demesne (noun)
an organization that is controlled by a dominant person or group	territory over which rule or control is exercised
the domain controlled by a feudal lord	extensive landed property (especially in the country) retained by the owner for his own use