demesne vs dukedom

demesne and dukedom both are nouns.

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

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

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