n.
Pronunciation: ' h ī -dr ə
Function: noun
Etymology: Middle English Ydra, from Latin Hydra, from Greek
Date: 15th century
1 : a many-headed serpent or monster in Greek mythology that was slain by Hercules and each head of which when cut off was replaced by two others
2 not capitalized : a multifarious evil not to be overcome by a single effort
3 [Latin (gen. Hydrae ), from Greek] : a southern constellation of great length that lies south of Cancer, Sextans, Corvus, and Virgo and is represented on old maps by a serpent
4 not capitalized [ New Latin, from Latin, Hydra] : any of numerous small tubular freshwater hydrozoan polyps ( Hydra and related genera) having at one end a mouth surrounded by tentacles