hydra hydra /ˈhaɪdrə/

noun

1. Small tubular solitary freshwater hydrozoan polyp  ( hydra )
   small tubular solitary freshwater hydrozoan polyp
    While examining pond water under the microscope, I was fascinated to observe a tiny hydra extending its tentacles.
   While examining pond water under the microscope, I was fascinated to observe a tiny hydra extending its tentacles.
   
   
2. Trouble that cannot be overcome by a single effort because of its many aspects or its persistent and pervasive quality  ( hydra )
   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
   we may be facing a hydra that defies any easy solution
   

 Hydra

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