Webster's English Dictionary

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hydra

Hy.dra \'hi--dr*\ n [ME Ydra, fr. L Hydra, fr. Gk] [L (gen. Hydrae), fr. 
   Gk] [NL, genus name, fr. L, Hydra] 1: a 9-headed serpent or monster of 
   Greek mythology slain by Hercules each  head of which when cut off is 
   replaced by two others unless the wound is cauterized not cap  2: a 
   multifarious evil not to be overcome by a single effort  3: a southern 
   constellation of great length that lies south of Cancer, Sext ans, Corvus, 
   and Virgo and is represented on old maps by a serpent not cap  4: any of 
   numerous small tubular freshwater hydrozoan polyps (as of the gen us Hydra)