1. (Greek mythology) monster with nine heads; when struck off each head was replaced by two new ones

- Hydra was slain by Hercules

Definition categories: person

2. a long faint constellation in the southern hemisphere near the equator stretching between Virgo and Cancer

Similar word(s): snake

Definition categories: object

3. 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

Definition categories: thought, problem, trouble

4. small tubular solitary freshwater hydrozoan polyp

Definition categories: animal, hydroid, hydrozoan