/huy"dreuh/ , n. , pl. hydras, hydrae /-dree/ for 1-3, gen. hydrae /-dree/ for 4.
1. ( often cap. ) Class. Myth. a water or marsh serpent with nine heads, each of which, if cut off, grew back as two; Hercules killed this serpent by cauterizing the necks as he cut off the heads.
2. any freshwater polyp of the genus Hydra and related genera, having a cylindrical body with a ring of tentacles surrounding the mouth, and usually living attached to rocks, plants, etc., but also capable of detaching and floating in the water.
3. a persistent or many-sided problem that presents new obstacles as soon as one aspect is solved.
4. ( cap. ) Astron. the Sea Serpent, a large southern constellation extending through 90° of the sky, being the longest of all constellations.
[ 1325-75; hýdra water serpent (r. ME ydre ]