last word vs dapperness

last word and dapperness both are nouns.

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

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

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

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