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Hy·dra

(hīdrə)

1. Greek Mythology The many-headed monster that was slain by Hercules.

2. Astronomy A satellite of Pluto.

3. A constellation in the equatorial region of the southern sky near Cancer, Libra, and Centaurus. Also called Snake².

4. A persistent or multifaceted problem that cannot be eradicated by a single effort.

[Middle English Idra, from Latin Hydra, fromGreekHudrā, Hydra, a water serpent; see wed-¹ in the Appendix of Indo-European roots.]

(click for a larger image)

Hydra

detail of a late 6th-century BC black-figure amphora depicting Hercules slaying the Hydra of Lerna

Indo-European & Semitic Roots Appendices

Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

Indo-European Roots

Semitic Roots

The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.

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