What is “a crenel”?

The story behind the answer

On a castle’s parapet, defenders stood behind battlements made of alternating solids and openings. The openings—the crenels—let soldiers observe, shoot arrows or bolts, and hurl missiles while using the adjacent solids (merlons) as cover. Their size and spacing balanced protection with fields of fire; some even had wooden shutters or temporary hoardings to improve defense.

‘Crenel’ comes from Old French (from Latin crena, notch) and gives us ‘crenellation’—the right or act of adding battlements, often granted by a medieval license to crenellate. By contrast, the raised solid is a merlon, the walkway behind is the wall-walk or chemin de ronde, and the narrow vertical shooting slit is a loophole or arrowslit.