The Collaborative International Dictionary of English v.0.48:

Emulsion \E*mul"sion\, n. [From L. emulgere, emulsum: cf. F.
   ['e]mulsion. See Emulge.]
   Any liquid preparation of a color and consistency resembling
   milk; as:
   (a) In pharmacy, an extract of seeds, or a mixture of oil and
       water united by a mucilaginous substance.
   (b) In photography, a liquid preparation of collodion holding
       salt of silver, used in the photographic process.
       [1913 Webster]

WordNet (r) 3.0 (2006):

emulsion
    n 1: (chemistry) a colloid in which both phases are liquids; "an
         oil-in-water emulsion"
    2: a light-sensitive coating on paper or film; consists of fine
       grains of silver bromide suspended in a gelatin [syn:
       emulsion, photographic emulsion]