1. chemically combined with water in its molecular form.
  2. (of paper pulp) beaten until gelatinous for making into water-resistant paper.

Origin of hydrated

First recorded in 1800–10; hydrate + -ed2
Related formsnon·hy·drat·ed, adjectiveun·hy·drat·ed, adjective


  1. any of a class of compounds containing chemically combined water. In the case of some hydrates, as washing soda, Na2CO3⋅10H2O, the water is loosely held and is easily lost on heating; in others, as sulfuric acid, SO3⋅H2O, or H2SO4, it is strongly held as water of constitution.
verb (used with or without object), hy·drat·ed, hy·drat·ing.
  1. to combine chemically with water.

Origin of hydrate

First recorded in 1795–1805; hydr-1 + -ate2
Related formshy·dra·tion, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for hydrated

Historical Examples of hydrated

British Dictionary definitions for hydrated


  1. (of a compound) chemically bonded to water molecules


  1. a chemical compound containing water that is chemically combined with a substance and can usually be expelled without changing the constitution of the substance
  2. a chemical compound that can dissociate reversibly into water and another compound. For example sulphuric acid (H 2 SO 4) dissociates into sulphur trioxide (SO 3) and water (H 2 O)
  3. (not in technical usage) a chemical compound, such as a carbohydrate, that contains hydrogen and oxygen atoms in the ratio two to one
  1. to undergo or cause to undergo treatment or impregnation with water
Derived Formshydration, nounhydrator, noun

Word Origin for hydrate

C19: from hydro- + -ate 1
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for hydrated



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)).



1850, "to form a hydrate;" 1947 as "to restore moisture;" from Greek hydr-, stem of hydor "water" (see water (n.1)) + -ate (2). Related: Hydrated; hydrating.

Online Etymology Dictionary, © 2010 Douglas Harper

hydrated in Medicine


  1. A solid compound containing water molecules combined in a definite ratio as an integral part of a crystal.
  1. To rehydrate.
  2. To supply water to a person or thing in order to restore or maintain fluid balance.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

hydrated in Science


  1. A compound produced by combining a substance chemically with water. Many minerals and crystalline substances are hydrates.
  1. To combine a compound with water, especially to form a hydrate.
  2. To supply water to a person in order to restore or maintain a balance of fluids.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.