white whale

/W AY1 T W EY1 L/
noun
  1. 1

    A cetacean, Delphinapterus leucas, found in the Arctic Ocean.

  2. 2

    An obsession; monomania.

  3. 3

    (trading cards) A printing plate used to manufacture a particular sports card, that is then issued as a collectible itself.

  4. 4

    A person who routinely spends very large amounts of money on gambling, investments, or premium content for video games etc.

Source: https://en.wiktionary.org/wiki/white%20whale