A minute freshwater coelenterate with a stalklike tubular body and a ring of tentacles around the mouth.
- Genus Hydra, class Hydrozoa
- The Phylum Cnidaria includes such diverse forms as jellyfish, hydra, sea anemones, and corals.
- The same is true for hydra, a freshwater cnidarian.
- There are some animals that don't belong to the Bilateria, though: members of the phylum Cnidaria, the jellyfish, hydra, sea anemones, and corals, which are typically radially symmetric.
1.1 (as noun hydra) A thing that is hard to overcome or resist because of its pervasive or enduring quality or its many aspects.
- Database scalability is a many-headed hydra that's hard to define, let alone tame.
- Yet it appears that multi-headed hydra, our scientific research establishment, is pulling in more than 200 different directions.
- We might have to strike back at some heads on this terrorist hydra, try not to slaughter innocents, and swallow the collateral damage.