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
   "The hydra regenerated its tentacles after they were cut off"

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

Derived forms: hydras

Type of: constellation, hydroid, hydrozoan, ill, mythical creature, mythical monster, prob [informal], problem, trouble

Part of: genus Hydra

Encyclopedia: Hydra, Greece