fleetingness vs transitoriness

fleetingness and transitoriness both are nouns.

Word	Noun	Adjective	Verb	Adverb
fleetingness	Yes	No	No	No
transitoriness	Yes	No	No	No

As nouns, transitoriness is a hypernym of fleetingness; that is, transitoriness is a word with a broader meaning than fleetingness:

fleetingness: the property of lasting for a very short time
transitoriness: an impermanence that suggests the inevitability of ending or dying

Other hypernyms of fleetingness include transience, transiency.

fleetingness (noun)	transitoriness (noun)
the property of lasting for a very short time	an impermanence that suggests the inevitability of ending or dying