‖n. pl. [ NL., from Gr. gna`qos the jaw + &unr_;, &unr_;, the mouth. ] (Zool.) A comprehensive division of vertebrates, including all that have distinct jaws, in contrast with the leptocardians and marsipobranchs (Cyclostoma), which lack them. [ Written also Gnathostomata. ] [ 1913 Webster ]