Hydra may refer to:

• Lernaean Hydra, a mythological many-headed serpent
• Hydra (constellation), the largest of the modern star constellations
• Hydra (moon), the third moon of the planet Pluto.
• Hydra (genus), a genus of simple fresh-water animals of the class Hydrozoa
• Hydra-Centaurus Supercluster, a supercluster of galaxies
• Hydra, Saronic Islands, a Greek island
• Hydra the Revenge, a roller coaster at Dorney Park

Hydra may also mean:

• HMS Hydra (A144), a Royal Navy deep ocean survey vessel
• Hydra (Atari), a 1990 arcade video game by Atari
• Hydra (chess), a chess computer
• Hydra (operating system), a distributed operating system
• Hydra (server), the name of the Beta Test Server of the XBOX 360 version of FFXI
• Hydra (software), a software used to test weak computer network passwords
• Hydra 70, an air-to-ground rocket
• The Hydra, a literary magazine once edited by Wilfred Owen
• Hydra Console, a forthcoming games console, in development by Andre LaMothe

Hydra may be a fictional name:

• San Andreas vehicle), a jet in the video game GTA: San Andreas
• HYDRA, a fictional secret criminal organization in the Marvel Universe
• Hydra, a space fighter in the video game series Colony Wars

• Hydra, one of two Legendary Air Ride machines in the video game Kirby Air Ride
• Mother Hydra, co-ruler of the Deep One race and consort of Father Dagon in the fictional Cthulhu mythos
• The Hydra, an Outer God in the fictional Cthulhu mythos
• The Hydra, Shao Kahn's animality in the Annihilation film
• A nickname for Hydralisk, a unit belonging to the Zerg race in the sci-fi strategy games Starcraft and Starcraft: Brood War
• The Spitting Hydra, a multi-targeting high-voltage electricity weapon in the popular Up Your Arsenal PS2 video game series.
• The Dualhead Hydra, a major enemy from Square's console role-playing game Final Fantasy Mystic Quest

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