What does "embrasure" mean?

Embrasure: (Arch.) A splay of a door or window. Apart, in the twilight gloom of a window's embrasure, Sat the lovers. Longfellow.

Additional senses

  1. 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.

Sources