Hydra

hī′dra, n. ( myth. ) a water-serpent with many heads, which when cut off were succeeded by others: any manifold evil: a genus of fresh-water polyps remarkable for their power of multiplication by being cut or divided.— adjs. Hy′dra-head′ed , difficulty to root out, springing up vigorously again and again; Hy′droid , like the hydra. [L.,—Gr. hydra — hydōr , water, akin to Sans. udras , an otter.]