demesne vs fiefdom

demesne and fiefdom both are nouns.

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

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

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