noun py??rox??y??lin \p??-??r??k-s??-l??n, p??-\Medical Definition of PYROXYLIN: a flammable mixture of cellulose nitrates usually with less than 12.5 percent nitrogen that is less explosive than guncotton, soluble in a mixture of ether and alcohol or other organic solvents, and used especially in making plastics and coatings (as lacquers)???see collodion Learn More About Dictionary: Definition of