The Collaborative International Dictionary of English v.0.48:

Iridescence \Ir`i*des"cence\, n. [See Iridescent.]
   Exhibition of colors like those of the rainbow, especially a
   surface reflection which changes color with the angle at
   which the object is viewed; the quality or state of being
   iridescent; a prismatic play of color; as, the iridescence of
   mother-of-pearl. It is due to interference of light waves
   reflected from the front and back surfaces of a thin layer
   transpatrent or semitransparent film.
   [1913 Webster]

WordNet (r) 3.0 (2006):

iridescence
    n 1: the visual property of something having a milky brightness
         and a play of colors from the surface [syn: opalescence,
         iridescence]