phosphorus A nonmetallic element used to manufacture phosphoric acid, in phosphor bronzes, incendiaries, pyrotechnics, matches, and rat poisons; the white or yellow allotrope is a soft waxy solid, soluble in carbon disulfide, insoluble in water and alcohol, and is poisonous and self-igniting in air; the red allotrope is an amorphous powder, insoluble in all solvents and is nonpoisonous; the black allotrope comprises lustrous crystals similar to graphite, and is insoluble in most solvents