(adj) so extremely old as seeming to belong to an earlier period, Syn. archaic, antiquated, Example:a ramshackle antediluvian tenement; antediluvian ideas; archaic laws
The Collaborative International Dictionary of English (GCIDE) v.0.53 Collaborative International Dictionary (GCIDE)
a. Of or relating to the period before the Deluge in Noah's time; hence, antiquated; as, an antediluvian vehicle. -- n. One who lived before the Deluge. [ 1913 Webster ]