%hypophosphorous%

a. [ Pref. hypo- + phosphorous. ] (Chem.) Pertaining to, or containing, phosphorus in a lower state of oxidation than in phosphoric compounds; as, hypophosphorous acid. [ 1913 Webster ]

Hypophosphorous acid (Chem.) , an acid, H3PO2, whose salts are produced by the action of barium hygrate on phosphorus. It may be obtained from its water solution, by exaporation and freezing, as a white crystalline substance. It is a powerful reducing agent. [ 1913 Webster ]