‖n. pl. [ NL., fr. Gr. chelw`nh a tortoise. ] (Zool.) An order of reptiles, including the tortoises and turtles, peculiar in having a part of the vertebræ, ribs, and sternum united with the dermal plates so as to form a firm shell. The jaws are covered by a horny beak. See Reptilia; also, Illust. in Appendix. [ 1913 Webster ]