What is "tetrahydrate"

n. (context chemistry English) A hydrate whose solid contains four molecules of water of crystallization per molecule, or per unit cell

A tetrahydrate is a molecule surrounded by four (4) molecules of water, forming a hydrate. The notation for a tetrahydrate is anhydrous molecule's formula·4HO, where the 4 represents tetrahydrate, and the HO represents the tetrahydrate. And the molecule's name changes to anhydrous molecule's name tetrahydrate.