Dor·mer or Dor·mer win·dow, n.  Arch. A window pierced in a roof, and so set as to be vertical while the roof slopes away from it. Also, the gablet, or houselike structure, in which it is contained.
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  dormer window
       n 1: the window in a gabled extension built to accommodate a
            window
       2: a gabled extension built out from a sloping roof to
          accommodate a vertical window [syn: dormer]