The Collaborative International Dictionary of English v.0.48:

Embrasure \Em*bra"sure\ (?; 135), n. [See Embrace.]
   An embrace. [Obs.] "Our locked embrasures." --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Embrasure \Em*bra"sure\ (277), n. [F., fr. embraser, perh.
   equiv. to ['e]braser to widen an opening; of unknown origin.]
   1. (Arch.) A splay of a door or window.
      [1913 Webster]

            Apart, in the twilight gloom of a window's
            embrasure,
            Sat the lovers.                       --Longfellow.
      [1913 Webster]

   2. (Fort.) An aperture with slant sides in a wall or parapet,
      through which cannon are pointed and discharged; a
      crenelle. See Illust. of Casemate.
      [1913 Webster]

WordNet (r) 3.0 (2006):

embrasure
    n 1: an opening (in a wall or ship or armored vehicle) for
         firing through [syn: port, embrasure, porthole]