Hydrus

name of the many-headed Lernaean water serpent slain by Herakles in Greek mythology, late 14c., idre, from Greek Hydra, fem. of hydros "water-snake," from hydor "water" (from suffixed form of PIE root *wed- (1) "water; wet").

The word is etymologically related to Sanskrit udrah "aquatic animal" and Old English ottur (see otter). Used figuratively for "any multiplicity of evils" [Johnson]. The fabulous beast's heads were said to grown back double when cut off. As a constellation (see Hydrus), usually identified as the monster Herakles slew, from mid-15c. As the genus name of a freshwater polyp from 1798; said to have been so called by Linnaeus for its regenerative capabilities.

Proto-Indo-European root meaning "water; wet."

It forms all or part of: abound; anhydrous; carbohydrate; clepsydra; dropsy; hydra; hydrangea; hydrant; hydrargyrum; hydrate; hydraulic; hydro-; hydrogen; hydrophobia; hydrous; Hydrus; inundate; inundation; kirsch-wasser; nutria; otter; redound; redundant; surround; undine; undulant; undulate; undulation; vodka; wash; water (n.1); wet; whiskey; winter.

It is the hypothetical source of/evidence for its existence is provided by: Hittite watar, Sanskrit udrah, Greek hydor, Old Church Slavonic and Russian voda, Lithuanian vanduo, Old Prussian wundan, Gaelic uisge "water;" Latin unda "wave;" Old English wæter, Old High German wazzar, Gothic wato "water."