Definition of hydras:
(n) :
(fantasy) A dragon-like creature with many heads and the ability to regrow them when maimed.
(n) :
(figurative) A complex, multifarious problem or situation that cannot be easily and rapidly solved.
(n) :
(biology) Any of several small freshwater polyps of the genus Hydra and related genera, having a naked cylindrical body and an oral opening surrounded by tentacles.
(n) :
(Greek mythology) A mythological serpent with many heads, slain by Hercules as one of his twelve labours.
(n) :
(astronomy) A spring constellation of the northern sky, said to resemble a serpent. It lies just south of the zodiac and contains the star Alphard.
(n) :
(astronomy) One of Pluto's moons.