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1. Trouble that cannot be overcome by a single effort because of its many aspects or its persistent and pervasive quality
   "we may be facing a hydra that defies any easy solution"
    
2. Small tubular solitary freshwater hydrozoan polyp

1. A long faint constellation in the southern hemisphere near the equator stretching between Virgo and Cancer
   - Snake
    
2. (Greek mythology) monster with nine heads; when struck off each head was replaced by two new ones
   "Hydra was slain by Hercules"

Derived forms: hydras

Type of: constellation, hydroid, hydrozoan, ill, mythical creature, mythical monster, problem, trouble

Part of: genus Hydra

Encyclopedia: Hydra, Saronic Islands