- a round, windowlike opening with a hinged, watertight glass cover in the side of a vessel for admitting air and light.
- an opening in a wall, door, etc., as one through which to shoot.
- a small aperture in the side of a vessel to admit light and air, usually fitted with a watertight glass or metal cover, or both
- an opening in a wall or parapet through which a gun can be fired; embrasure
