diskn.[L. discus, Gr. di`skos. See Dish.]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.) The whole surface of a leaf.()6. (Zol.) The anterior surface or oral area of clenterate animals, as of sea anemones.()Disk engine, a form of rotary steam engine. -- Disk shell (Zol.), any species of Discina.()