Embrasure

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.

The walls are slitted with embrasures through which bowmen could fire, indicating that the belfry also served as a stronghold during border skirmishes.

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

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.

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: