antediluvian vs antediluvial

antediluvian is a noun but antediluvial is not a noun.

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

As adjectives, antediluvian and antediluvial are synonyms defined as:

antediluvian and antediluvial: of or relating to the period before the biblical flood

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

antediluvian (adjective)	antediluvial (adjective)
of or relating to the period before the biblical flood	of or relating to the period before the biblical flood
so extremely old as seeming to belong to an earlier period