Illustrated Glossary of Organic Chemistry

Hydrate: (1) A substance that contains water molecule(s) within its structure. When one molecule of water is present, the molecule is a monohydrate. Two molecules of water comprise a dihydrate, etc.

Molecular formula
CaSO4 . 1/2 H2O Calcium sulfate hemihydrate
NaRuO4 . H2O
Sodium perruthenate monohydrate
CaSO4 . 2 H2O Calcium sulfate dihydrate
NaC2H3O2 . 3 H2O Sodium acetate trihydrate
FeCl2 . 4 H2O Iron (II) chloride tetrahydrate
CuSO4 . 5 H2O Copper (II) sulfate pentahydrate
FeBr3 . 6 H2O Iron (III) bromide hexahydrate

(2) The process of gaining water (hydration). The process of losing water is to dehydrate.