Tutoring chemistry, the term anhydride may pop up.

An anhydride is a molecule that results from the removal of water.

An acid anhydride will assume its acidic tendency if water is added. Nonmetal oxides typically are acid anhydrides – for example, SO₃:

SO₃ + H₂O → H₂SO₄

Metal oxides are typically base anhydrides:

CaO + H₂O → Ca²⁺ + 2OH^–

Source:

Mortimer, Charles E. Chemistry, sixth ed. Belmont: Wadsworth, 1986.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.