water serpent
/ˈwɔːtə ˌsəːp(ə)nt/noun
1A sea serpent or other mythical aquatic creature. Formerly also: a water snake or sea snake.
2 Astronomy. With capital initials. The southern constellation Hydra.
- Now chiefly as a gloss of the name Hydra..
Origin
Mid 16th century; earliest use found in John Palsgrave (d. 1554), teacher and scholar of languages. From water + serpent.