Source : Webster's Revised Unabridged Dictionary (1913)

Disk \Disk\, n. [L. discus, Gr. ?. See {Dish}.] [Written also
   {disc}.]
   1. A discus; a quoit.

            Some whirl the disk, and some the javelin dart.
                                                  --Pope.

   2. A flat, circular plate; as, a disk of metal or paper.

   3. (Astron.) The circular figure of a celestial body, as seen
      projected of the heavens.

   4. (Biol.) A circular structure either in plants or animals;
      as, a blood disk; germinal disk, etc.

   5. (Bot.)
      (a) The whole surface of a leaf.
      (b) The central part of a radiate compound flower, as in
          sunflower.
      (c) A part of the receptacle enlarged or expanded under,
          or around, or even on top of, the pistil.

   6. (Zo["o]l.)
      (a) The anterior surface or oral area of c[oe]lenterate
          animals, as of sea anemones.
      (b) The lower side of the body of some invertebrates,
          especially when used for locomotion, when it is often
          called a creeping disk.
      (c) In owls, the space around the eyes.

   {Disk engine}, a form of rotary steam engine.

   {Disk shell} (Zo["o]l.), any species of Discina.