The Collaborative International Dictionary of English v.0.48:

Collodion \Col*lo"di*on\, n. [Gr. ? like glue; ko`lla glue + ?
   form. Cf. Colloid.] (Chem.)
   A solution of pyroxylin (soluble gun cotton) in ether
   containing a varying proportion of alcohol. It is strongly
   adhesive, and is used by surgeons as a coating for wounds;
   but its chief application is as a vehicle for the sensitive
   film in photography.
   [1913 Webster]

   Collodion process (Photog.), a process in which a film of
      sensitized collodion is used in preparing the plate for
      taking a picture.

   Styptic collodion, collodion containing an astringent, as
      tannin.
      [1913 Webster]

WordNet (r) 3.0 (2006):

collodion
    n 1: a colorless syrupy solution of pyroxylin in ether and
         alcohol; used as a coating for wounds or photographic films