Lewis & Short

† ĕchidna, ae, f., = ἔχιδνα,

  1. I. an adder, viper. The Furies were said to have them twined in their hair; hence: stipite te Stygio tumidisque adflavit Echidnis E tribus una soror, Ov. M. 10, 313.
  2. II. Nom. prop.
    1. A. Lernaea, the Lernaean hydra, killed by Hercules, Ov. M. 9, 69; 158; id. F. 5, 405.
    2. B. A monster, half woman and half serpent, the mother of Cerberus, Ov. M. 4, 501.
      Hence, Echidnēus, a, um, adj., of Echidna: canis, i. e. Cerberus, Ov. M. 7, 408.