1802, "compound of water and another chemical," from French hydrate, coined c.1800 by French chemist Joseph-Louis Proust (1754-1826) from Greek hydr-, stem of hydor "water" (see water (n.1)).
hydrate hy·drate (hī'drāt')
A solid compound containing water molecules combined in a definite ratio as an integral part of a crystal. v. hy·drat·ed, hy·drat·ing, hy·drates
To supply water to a person or thing in order to restore or maintain fluid balance.