transiency vs fugacity

transiency and fugacity both are nouns.

Word	Noun	Adjective	Verb	Adverb
transiency	Yes	No	No	No
fugacity	Yes	No	No	No

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

transiency: an impermanence that suggests the inevitability of ending or dying
fugacity: the lack of enduring qualities (used chiefly of plant parts)

Other hyponyms of transiency include fugaciousness, ephemerality, ephemeralness, fleetingness.

transiency (noun)	fugacity (noun)
an impermanence that suggests the inevitability of ending or dying	the lack of enduring qualities (used chiefly of plant parts)
	the tendency of a gas to expand or escape