disk

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A thin, flat, circular object or plate.
• noun Something resembling such an object.
• noun The disk used in a disc brake.
• noun A disk used on a disk harrow.
• noun A round, flattened structure in a plant or animal, such as an intervertebral disk.
• noun Botany The central area bearing numerous disk flowers in the flower head of a composite plant such as a daisy.
• noun An optical disc, especially a compact disc.
• noun A magnetic disk, such as a floppy disk or hard disk.
• noun The data stored on such objects.
• noun A phonograph record.
• noun A circular grid in a phototypesetting machine.
• transitive verb To work (soil) with a disk harrow.
• transitive verb To make (a recording) on a phonograph record.

from The Century Dictionary.

• noun A small medicated gelatin tablet about of an inch thick, which contains a small amount of glycerin to prevent it from becoming hard and brittle: a simple means of applying accurately adjusted quantities of mydriatic, myotic, and anesthetic alkaloids such as atropin, physostigmine, and cocaïne to the eye.
• In agriculture, to cultivate with a disk-cultivator.
• noun Same as discus, 1.
• noun In the Gr. Ch., a paten.
• noun 3. Any flat, or approximately or apparently flat, circular plate or surface.
• noun Specifically In botany: The flat surface of an organ, such as a leaf, in distinction from the margin.
• noun Any flat, circular, discus-shaped growth, as the adhesive disks which form on the tendrils of the Virginia creeper.
• noun In the tubuliflorous Compositæ, the series of flowers having a tubular corolla, and forming the central portion or whole of the head, as distinct from a surrounding ligulate-flowered ray; also, the central portion of any radiate inflorescence
• noun An enlargement of the torus of a flower about the pistil.
• noun A name sometimes given to the bordered pits (otherwise called dots and discoid markings) which characterize the woody tissue of gymriosperms, as the pine.
• noun The hymenium of a discocarp; the cup-like or otherwise expanded surface on which the asci are borne in Discomycetes.
• noun In zoöl, and anatomy, any flattened and rounded surface or part; a discus.
• noun In armor, same as roundel.
• noun One of the collars separating and securing the cutters on a horizontal mandrel.

from the GNU version of the Collaborative International Dictionary of English.

• noun A discus; a quoit.
• noun A flat, circular plate.
• noun (Astron.) The circular figure of a celestial body, as seen projected of the heavens.
• noun (Biol.) A circular structure either in plants or animals
• noun The whole surface of a leaf.
• noun The central part of a radiate compound flower, as in sunflower.
• noun A part of the receptacle enlarged or expanded under, or around, or even on top of, the pistil.
• noun The anterior surface or oral area of cœlenterate animals, as of sea anemones.
• noun The lower side of the body of some invertebrates, especially when used for locomotion, when it is often called a creeping disk.
• noun In owls, the space around the eyes.
• noun a form of rotary steam engine.
• noun (Zoöl.) any species of Discina.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A thin, flat, circular plate or similar object.
• noun figuratively Something resembling a disk.
• noun dated A vinyl phonograph/gramophone record.
• noun computing A floppy disk - removable magnetic medium or a hard disk - fixed, persistent digital storage.
• noun computing, nonstandard A disc - either a CD-ROM, an audio CD, a DVD or similar removable storage medium.
• noun agriculture A harrow.