n. In classical antiquity, a circular piece of stone or plate of metal, about 12 inches in diameter, pitched from a fixed point to the greatest possible distance, as a gymnastic exercise and as an athletic contest.n. In anatomy, physical, zoology, and botany, a disk of any kind.n. [capitalized] In zoöl.: A genus of mollusks, A genus of acalephs.n. A genus of scombroid fishes.