noun

• 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.
• (fantasy) A dragon-like creature with many heads and the ability to regrow them when maimed.
• A complex, multifarious problem or situation that cannot be solved easily and rapidly.
• (Greek mythology) A mythological serpent with many heads, slain by Hercules as one of his twelve labours.
• (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.
• (astronomy) One of Pluto's moons.
• One of the Saronic Islands in the Aegean Sea.
• (geography) A commune in Algiers Province, Algeria.