Hȳdra, ae, f., = Ὕδρα [kindred with Sanscr. udri; Ang.-Sax. oter, otor; Engl. and Germ. Otter; cf. also the Gr. ἔνυδρις],
I the water-serpent killed by Hercules near the Lernean Lake , the Hydra , with seven heads; as fast as one of them was cut off two sprang up in its stead; it is also called Echidna: Lernaea pestis, Hydra, Lucr. 5, 27; Ov. M. 9, 192; Hor. C. 4, 4, 61; id. Ep. 2, 1, 10; Hyg. Fab. 30; 34; 151. As identified with Echidna, the mother of Cerberus , Cic. poët. Tusc. 2, 9, 22.—Prov.: vide ne in istis duobus generibus hydra tibi sit et pellis, Hercules autem et alia opera majora, in illis rebus, quas praetermittis, relinquantur, i. e. the easiest , the least important , Cic. de Or. 2, 17, 71.—
B Deriv. Hȳdraeus , a, um, adj., of or belonging to the Hydra : germen, Mart. Cap. 7, 237.—
II Transf.
A The constellation of the Water-snake , also called Anguis, Cic. Arat. 214 (also id. N. D. 2, 44, 114); Hyg. Astr. 2, 40; 3, 39.—
B Acc. to Verg., a hydra with fifth heads , that keeps watch at the gates of the Lower World , Verg. A. 6, 576.