/pen tok"suyd, -sid/ , Chem.
a white, deliquescent, crystalline powder, P 2 O 5 , that, depending upon the amount of water it absorbs, forms orthophosphoric acid, metaphosphoric acid, or pyrophosphoric acid, produced by the burning of phosphorus in dry air: used in the preparation of phosphoric acids, as a drying and dehydrating agent, and in organic synthesis. Also called phosphoric anhydride .