a. [ Gr. pla`x, plako`s, a tablet + -oid. ] (Zool.) Platelike; having irregular, platelike, bony scales, often bearing spines; pertaining to the placoids. [ 1913 Webster ]

n. (Zool.) (a) Any fish having placoid scales, as the sharks. (b) One of the Placoides. [ 1913 Webster ]

‖n. pl. [ NL. ] (Zool.) A group of fishes including the sharks and rays; the Elasmobranchii; -- called also Placoidei. [ 1913 Webster ]

n. (Zool.) One of the placoids. [ 1913 Webster ]