- hydra
- 1835, genus name of a freshwater polyp, from Gk. Hydra, many-headed Lernaean water serpent slain by Hercules (this sense is attested in Eng. from late 14c.), from hydor (gen. hydatos) "water" (see water (n.1)); related to Skt. udrah "aquatic animal" and O.E. ottur "otter." Used figuratively for "any multiplicity of evils" [Johnson].