Echidna \E*chid"na\, n. [L., a viper, adder, Gr. ?.] 1. (Gr. Myth.) A monster, half maid and half serpent. 2. (Zo["o]l.) A genus of {Monotremata} found in Australia, Tasmania, and New Guinea. They are toothless and covered with spines; -- called also {porcupine ant-eater}, and {Australian ant-eater}.