A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used.

What does it mean if something is anhydrous?

: free from water and especially water of crystallization.

What does it mean when a chemical is anhydrous?

Anhydrous, an-hī′drus, adj. a term applied to a chemical substance free from water.