antediluvial vs antediluvian

antediluvial is not a noun while antediluvian is a noun.

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

As adjectives, antediluvial and antediluvian are synonyms defined as:

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

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

antediluvial (adjective)	antediluvian (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