NOUN (1)

1. any compound that contains water of crystallization;


VERB (3)

1. supply water or liquid to in order to maintain a healthy balance;
- Example: "the bicyclists must be hydrated frequently"

2. become hydrated and combine with water;

3. cause to be hydrated; add water or moisture to;
- Example: "hydrate your skin"

The Collaborative International Dictionary of English v.0.48:

Hydrate \Hy"drate\, n. [Gr. "y`dwr water: cf. F. hydrate.]
   (Chem.)
   (a) A compound formed by the union of water with some other
       substance, generally forming a neutral body, as certain
       crystallized salts.
   (b) A substance which does not contain water as such, but has
       its constituents (hydrogen, oxygen, hydroxyl) so arranged
       that water may be eliminated; hence, a derivative of, or
       compound with, hydroxyl; hydroxide; as, ethyl hydrate, or
       common alcohol; calcium hydrate, or slaked lime.
       [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Hydrate \Hy"drate\, v. t. [imp. & p. p. Hydrated; p. pr. & vb.
   n. Hydrating.]
   To form into a hydrate; to combine with water.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hydrate
    n 1: any compound that contains water of crystallization
    v 1: supply water or liquid to in order to maintain a healthy
         balance; "the bicyclists must be hydrated frequently"
    2: become hydrated and combine with water
    3: cause to be hydrated; add water or moisture to; "hydrate your
       skin" [ant: dehydrate, desiccate, dry up, exsiccate]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "hydrate":
   acetify, acidify, acidulate, alkalify, alkalize, borate, carbonate,
   catalyze, chemical, chlorinate, electrolyze, ferment,
   homopolymerize, hydrogenate, hydroxylate, isomerize, nitrate,
   oxidize, pepsinate, peroxidize, phosphatize, polymerize, reduce,
   sulfate, sulfatize, sulfonate, work