ephemeralness vs transience

ephemeralness and transience both are nouns.

Word	Noun	Adjective	Verb	Adverb
ephemeralness	Yes	No	No	No
transience	Yes	No	No	No

As nouns, transience is a hypernym of ephemeralness; that is, transience is a word with a broader meaning than ephemeralness:

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

Other hypernyms of ephemeralness include transiency, transitoriness.

ephemeralness (noun)	transience (noun)
the property of lasting for a very short time	an impermanence that suggests the inevitability of ending or dying
	the attribute of being brief or fleeting