The Collaborative International Dictionary of English v.0.48:

Transparency \Trans*par"en*cy\, n.; pl. Transparencies. [Cf.
   F. transparence.]
   1. The quality or condition of being transparent;
      transparence.
      [1913 Webster]

   2. That which is transparent; especially, a picture painted
      on thin cloth or glass, or impressed on porcelain, or the
      like, to be viewed by natural or artificial light, which
      shines through it. --Fairholt.
      [1913 Webster]

WordNet (r) 3.0 (2006):

transparency
    n 1: permitting the free passage of electromagnetic radiation
         [syn: transparency, transparence] [ant: opacity]
    2: the quality of being clear and transparent [syn:
       transparency, transparence, transparentness]
    3: picture consisting of a positive photograph or drawing on a
       transparent base; viewed with a projector [syn: foil,
       transparency]

Moby Thesaurus II by Grady Ward, 1.0:

112 Moby Thesaurus words for "transparency":
   Celluloid, Lucite, Perspex, Photostat, Plexiglas, Telephoto,
   Wirephoto, Xerox, Xerox copy, aerial photograph, aquamarine, beryl,
   black-and-white photograph, blowup, blueprint, candid photograph,
   carnelian, cellophane, chalcedony, cheesecake, chiffon,
   chronophotograph, chrysolite, citrine, clarity, clear-cutness,
   clearness, coherence, color photograph, color print, connectedness,
   consistency, contact printing, crystal, crystallinity, cyanotype,
   definition, diamond, diaphane, diapositive, directness,
   distinctness, emerald, enlargement, explicitness, glossy, gossamer,
   heliochrome, heliograph, hologram, hyaline, lantern slide,
   limpidity, lucidity, matte, mica, microcopy, microprint, montage,
   moonstone, morganite, mug, mug shot, onionskin, pellucidity,
   perspicuity, photo, photobiography, photochronograph, photocopy,
   photograph, photogravure, photomap, photomicrograph, photomontage,
   photomural, photostatic copy, picture, pinup, plain English,
   plain speech, plain style, plainness, portrait, positive, print,
   projection printing, quartz, semi-matte, sheers, shot, simplicity,
   slide, snap, snapshot, still, still photograph,
   straightforwardness, structure, telephotograph, tissue,
   tissue paper, transparent things, transpicuity, unadorned style,
   unambiguousness, unequivocalness, unmistakableness, veil, voile,
   water, window