a. [ NL. etheostoma name of a genus + -oid. ] (Zoöl.) Pertaining to, or like, the genus Etheostoma. -- n. Any fish of the genus Etheostoma and related genera, allied to the perches; -- also called darter. The etheostomoids are small and often bright-colored fishes inhabiting the fresh waters of North America. About seventy species are known, including the rare snail darter (Percina tanasi), 3 inches long, found only in the Tennessee River and classified as a threatened species. See Darter. [ 1913 Webster ]