demesne vs fief

demesne and fief both are nouns.

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

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

demesne: extensive landed property (especially in the country) retained by the owner for his own use
fief: a piece of land held under the feudal system

demesne (noun)	fief (noun)
territory over which rule or control is exercised	a piece of land held under the feudal system
extensive landed property (especially in the country) retained by the owner for his own use