Source : Webster's Revised Unabridged Dictionary (1913)

   1. The hard, white, opaque, fine-grained substance
      constituting the tusks of the elephant. It is a variety of
      dentine, characterized by the minuteness and close
      arrangement of the tubes, as also by their double flexure.
      It is used in manufacturing articles of ornament or
      utility.

   Note: Ivory is the name commercially given not only to the
         substance constituting the tusks of the elephant, but
         also to that of the tusks of the hippopotamus and
         walrus, the hornlike tusk of the narwhal, etc.

   2. The tusks themselves of the elephant, etc.

   3. Any carving executed in ivory. --Mollett.

   4. pl. Teeth; as, to show one's ivories. [Slang]

   {Ivory black}. See under {Black}, n.

   {Ivory gull} (Zo["o]l.), a white Arctic gull ({Larus
      eburneus}).

   {Ivory nut} (Bot.), the nut of a species of palm, the
      {Phytephas macroarpa}, often as large as a hen's egg. When
      young the seed contains a fluid, which gradually hardness
      into a whitish, close-grained, albuminous substance,
      resembling the finest ivory in texture and color, whence
      it is called {vegetable ivory}. It is wrought into various
      articles, as buttons, chessmen, etc. The palm is found in
      New Grenada. A smaller kind is the fruit of the {Phytephas
      microarpa}. The nuts are known in commerce as Corosso
      nuts.

   {Ivory palm} (Bot.), the palm tree which produces ivory nuts.
      

   {Ivory shell} (Zo["o]l.), any species of {Eburna}, a genus of
      marine gastropod shells, having a smooth surface, usually
      white with red or brown spots.

   {Vegetable ivory}, the meat of the ivory nut. See {Ivory nut}
      (above).

Source : WordNet®

ivory nut
     n : nutlike seed of a South American palm; the hard white shell
         takes a high polish and is used for e.g. buttons [syn: {vegetable
         ivory}, {apple nut}]