embrasure

Any of the indentations between the merlons of a battlement; an opening in a wall or parapet through which ordnance can be fired.

Near-synonym: crenel (sometimes hyponymous technically)

But there were less casualties than might have been expected, and the barricade rose steadily, a wall of concrete two feet thick, with embrasures for two machine-guns and a small field gun.

Any small protected space.

She had a special seat there, a little embrasure between two upright slabs of sandstone, which was sheltered and private.

The slanting indentation in a wall for a door or window, such that the space is larger on the inside than the outside.

When the fit had spent itself he walked weakly to the window and, lifting the sash, sat in a corner of the embrasure and leaned his elbow upon the sill.

Now he stands in a window embrasure, Liz's prayer book in hand.

An embrace.

And suddenly; where injury of chance / Puts back leave-taking, justles roughly by / All time of pause, rudely beguiles our lips / Of all rejoindure, forcibly prevents / Our lock'd embrasures, strangles our dear vows / Even in the birth of our own labouring breath: