Existing or occurring before the Flood described in the biblical book of Genesis, or (in later use) before a widespread flood as described in other mythological traditions; of or relating to the period before such a flood.

Earlier or older than a period of deposition of diluvial or drift deposits. Now chiefly historical.

Of animals, plants, etc.: prehistoric; long extinct; such as are known only from their fossil remains.

Very antiquated; ridiculously old-fashioned or out-of-date; = "antediluvian". Now somewhat rare.