Definify.com
Webster 1913 Edition
Hydrate
Hy′drate
,Noun.
 [Gr. 
ὕδωρ 
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.Hy′drate
,Verb.
 T.
 [
imp. & p. p. 
Hydrated
; p. pr. & vb. n. 
Hydrating
.] To form into a hydrate; to combine with water. 
Webster 1828 Edition
Hydrate
HY'DRATE
,Noun.
 A hydrate is a substance which has formed so intimate a union with water as to solidify it, and render it a component part. 
Slaked lime is a hydrate of lime.