adj

• (biblical) Belonging or pertaining to, or existing in, the time prior to the great flood described in Genesis, or (by extension) to a great or destructive flood or deluge described in other mythologies.
  "[P]erhaps ſome perſons might outlive Methuſelah; the Text intending onely the maſculine line of Seth, conduceable unto the Genealogy of our Saviour, and the antediluvian Chronology."
• (by extension) Of animals and plants: long extinct; prehistoric.
  "Having already described him [the whale] in most of his present habitatory and anatomical peculiarities, it now remains to magnify him in an archæological, fossiliferous, and antediluvian point of view."
• (figurative, hyperbolic, chiefly humorous)
  "[H]is eldest son Bo-bo, […] let some sparks escape into a bundle of straw, which kindling quickly, spread the conflagration over every part of their poor mansion, till it was reduced to ashes. Together with the cottage (a sorry antediluvian make-shift of a building, you may think it), what was of much more importance, a fine litter of new-farrowed pigs, no less than nine in number, perished."
• (figurative, hyperbolic, chiefly humorous)
  "Those ideas are antediluvian."

noun

• (biblical) A person who lived in the time prior to the great flood described in Genesis, especially one of the biblical patriarchs.
• (figurative, hyperbolic, chiefly humorous)
  "From what cursed old antediluvian, who lived before the invention of the spinning-jennies, she learned this craft, Heaven only knows; […]"
• (figurative, hyperbolic, chiefly humorous)