last word vs jauntiness

last word and jauntiness both are nouns.

Word	Noun	Adjective	Verb	Adverb
last word	Yes	No	No	No
jauntiness	Yes	No	No	No

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

Other hyponyms of last word include dapperness, nattiness, rakishness.

last word (noun)	jauntiness (noun)
elegance by virtue of being fashionable	stylishness as evidenced by a smart appearance
the final statement in a verbal argument	a breezy liveliness
an authoritative statement