archaic vs antediluvian

archaic is not a noun while antediluvian is a noun.

Word	Noun	Adjective	Verb	Adverb
archaic	No	Yes	No	No
antediluvian	Yes	Yes	No	No

As adjectives, archaic and antediluvian are synonyms defined as:

archaic and antediluvian: so extremely old as seeming to belong to an earlier period

Other synonyms of archaic include antiquated.

archaic (noun)	antediluvian (noun)
	a very old person
	any of the early patriarchs who lived prior to the Noachian deluge

archaic (adjective)	antediluvian (adjective)
little evolved from or characteristic of an earlier ancestral type	of or relating to the period before the biblical flood
so extremely old as seeming to belong to an earlier period	so extremely old as seeming to belong to an earlier period