antediluvian vs ancient

antediluvian and ancient both are nouns.

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

As nouns, antediluvian and ancient are synonyms defined as:

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

antediluvian (adjective)	ancient (adjective)
of or relating to the period before the biblical flood	very old
so extremely old as seeming to belong to an earlier period	belonging to times long past especially of the historical period before the fall of the Western Roman Empire