antediluvian vs archaic

antediluvian is a noun but archaic is not a noun.

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

As adjectives, antediluvian and archaic are synonyms defined as:

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

Other synonyms of antediluvian include antiquated.

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

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