adjective 1. Of or relating to the period before the Biblical flood. 2. very old, old-fashioned, or out of date; antiquated; primitive: antediluvian ideas.
The other thing that almost always goes with these myths is the notion of an antediluvian civilisation -- something which existed before the flood and was destroyed by it. -- Graham Hancock, The Guardian
Antediluvian is related to the Latin term dīluvium meaning "a flood." The prefix ante- means "before" and is used in the formation of compound words.