imperium vs demesne

imperium and demesne both are nouns.

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

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

imperium: the domain ruled by an emperor or empress; the region over which imperial dominion is exercised
demesne: territory over which rule or control is exercised

Other hypernyms of imperium include domain, land.

imperium (noun)	demesne (noun)
supreme authority; absolute dominion	territory over which rule or control is exercised
the domain ruled by an emperor or empress; the region over which imperial dominion is exercised	extensive landed property (especially in the country) retained by the owner for his own use