Entry 1 sense Webster, 1913 Gymnochroa /(jĭm*nŏk"rō̇*ȧ)/ · Gym·noch·ro·a · IPA 01 n. pl. A division of Hydroidea including the hydra. See Hydra. 1. A division of Hydroidea including the hydra. See Hydra.(Zool.) See: Hydra