[ hahy-dreyt ]
/ ˈhaɪ dreɪt /


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.

to combine chemically with water.

Origin of hydrate

First recorded in 1795–1805; hydr-1 + -ate2


hy·dra·tion, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

Example sentences from the Web for hydration

British Dictionary definitions for hydration

/ (ˈhaɪdreɪt) /


a chemical compound containing water that is chemically combined with a substance and can usually be expelled without changing the constitution of the substance
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)
(not in technical usage) a chemical compound, such as a carbohydrate, that contains hydrogen and oxygen atoms in the ratio two to one


to undergo or cause to undergo treatment or impregnation with water

Derived forms of hydrate

hydration, 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

Medical definitions for hydration (1 of 2)

[ hī-drāshən ]


The addition of water to a chemical molecule without hydrolysis.
The process of providing an adequate amount of liquid to bodily tissues.

Medical definitions for hydration (2 of 2)

[ hīdrāt′ ]


A solid compound containing water molecules combined in a definite ratio as an integral part of a crystal.


To rehydrate.
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.

Scientific definitions for hydration

[ hīdrāt′ ]


A compound produced by combining a substance chemically with water. Many minerals and crystalline substances are hydrates.


To combine a compound with water, especially to form a hydrate.
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.