noun
: a compound known in various polymeric forms (P 2 O 5 ) x (as the dimer P 4 O 10 in the vapor and one crystalline modification) that is obtained usually by burning phosphorus in an excess of dry air and occurs as a white powder that reacts vigorously and sometimes explosively with water to form phosphoric acids irritating to the skin and mucous membranes, and is used chiefly as a drying agent, as a condensing agent in organic synthesis, and in making phosphoric acids and derivatives; di-phosphorus pentoxide — called also phosphoric anhydride