1. of or relating to the period before the biblical flood - antediluvian man • Syn: antediluvial • Pertains to noun: diluvial (for: antediluvial), diluvial • Derivationally related forms: antediluvian (for: antediluvial) 2. so extremely old as seeming to belong to an earlier period - a ramshackle antediluvian tenement - antediluvian ideas - archaic laws • Syn: antiquated, archaic • Similar to: old