\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.