†(a) A marine fish with distinctive markings, (probably) the striped sea bream, Lithognathus mormyrus. Obsolete. (b) (In later use) any fish of the genus Mormyrus (family Mormyridae), comprising African freshwater fishes with curved elongate snouts and weak electric organs; an elephant-snout fish; (in form Mormyrus) the genus itself.
Early 18th century; earliest use found in Phillips's New World of Words. From post-classical Latin mormyrus, also mormyra from ancient Greek μορμύρος a kind of sea bream, probably from μορμύρειν on account of the sound made by the fish.