The Collaborative International Dictionary of English v.0.48:

Windowpane \Win"dow*pane`\, n.
   1. (Arch.) See Pane, n., (3)
      b . [In this sense, written also window pane.]
        [1913 Webster]

   2. (Zool.) A thin, spotted American turbot (Pleuronectes
      maculatus) remarkable for its translucency. It is not
      valued as a food fish. Called also spotted turbot,
      daylight, spotted sand flounder, and water flounder.
      [1913 Webster]

WordNet (r) 3.0 (2006):

windowpane
    n 1: a pane of glass in a window; "the ball shattered the
         window" [syn: windowpane, window]
    2: very thin translucent flounder of the Atlantic coast of North
       America [syn: windowpane, Scophthalmus aquosus]

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "windowpane":
   bay, bay window, bow window, casement, casement window, diaphane,
   display case, fan window, fanlight, glass, glassware, grille,
   lancet window, lantern, lattice, light, louver window, oriel, pane,
   picture window, port, porthole, rose window, shopwindow, showcase,
   skylight, stemware, transom, transparent substance, vitrics,
   vitrine, watch crystal, watch glass, wicket, window, window bay,
   window glass, windowlight