anhydrideChem.|ænˈhaɪdraɪd|[mod.f.Gr.ἄνῡδρ-ος waterless (f.ἀνpriv.+ ὕδωρ water) + -ide.]A chemical compound formed by the union of oxygen with another element, without hydrogen, but which, on exposure to water, absorbs hydrogen and becomes an acid. Also called anhydrous acids, because they are produced by expelling the water (containing all the hydrogen) from oxy-acids.1863WattsDict.Chem.I. 295Very few triatomic anhydrides are yet known. Phosphoric anhydride, P₂O₅, is the only well known member of this class.1869Eng.Mech.9 Apr. 58/2Sulphuric anhydride SO₃ when added to water, takes up the oxygen to form a new acid radical.