The Collaborative International Dictionary of English v.0.48:

pyroxylin \py*rox"y*lin\, n. (Chem.)
   A substance resembling gun cotton in composition and
   properties, but distinct in that it is more highly nitrified
   and is soluble in alcohol, ether, etc.; -- called also
   pyroxyle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

pyroxylin
    n 1: highly flammable nitrocellulose used in making collodion
         and plastics and lacquers [syn: pyroxylin, pyroxyline]