1. A discus; a quoit.
  2. A flat, circular plate; as, a disk of metal or paper.
  3. The circular figure of a celestial body, as seen projected of the heavens.
  4. A circular structure either in plants or animals; as, a blood disk; germinal disk, etc.
  5. The whole surface of a leaf.
  6. The central part of a radiate compound flower, as in sunflower.
  7. A part of the receptacle enlarged or expanded under, or around, or even on top of, the pistil.
  8. The anterior surface or oral area of coelenterate animals, as of sea anemones.
  9. The lower side of the body of some invertebrates, especially when used for locomotion, when it is often called a creeping disk.
  10. In owls, the space around the eyes.