Lewis & Short

† 1. hydrus or -os, i, m., = ὕδρος, a water-serpent, serpent (cf.: chelydrus, chersydrus, anguis, serpens).

  1. I. Lit., Plin. 29, 4, 22, § 72; Verg. G. 4, 458; id. A. 7, 753; Ov. M. 13, 804: marini, Plin. 6, 23, 26, § 98. In the hair of the Furies, of Medusa, etc., Verg. A. 7, 447; Val. Fl. 2, 195; Ov. M. 4, 800; hence poet. transf.: nam si Vergilio puer et tolerabile desit Hospitium, caderent omnes a crinibus hydri, i. e. all his poetic fire would have come to naught (referring to his description of the Furies, A. 7, 415 and 447), Juv. 7, 70.
  2. II. Transf.
    1. A. The poison of a serpent, Sil. 1, 322.
    2. B. Hydros, i, the constellation of the Waterserpent, called also Anguis and Hydra, German. Arat. 429.