last word vs elegance

last word and elegance both are nouns.

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

As nouns, elegance is a hypernym of last word; that is, elegance is a word with a broader meaning than last word:

last word (noun)	elegance (noun)
elegance by virtue of being fashionable	a refined quality of gracefulness and good taste
the final statement in a verbal argument	a quality of neatness and ingenious simplicity in the solution of a problem (especially in science or mathematics)
an authoritative statement