donjon vs fastness

donjon and fastness both are nouns.

Word	Noun	Adjective	Verb	Adverb
donjon	Yes	No	No	No
fastness	Yes	No	No	No

As nouns, fastness is a hypernym of donjon; that is, fastness is a word with a broader meaning than donjon:

Other hypernyms of donjon include stronghold.

donjon (noun)	fastness (noun)
the main tower within the walls of a medieval castle or fortress	a strongly fortified defensive structure
	a rate (usually rapid) at which something happens
	the quality of being fixed in place as by some firm attachment