With alternating projections and indentations, with right angles between the two.
The top of a castle tower is usually crenellated; that is, the perimeter of its battlements forms a repeating pattern of thick stone, gap, thick stone, gap, and so on, thus affording both protection and a view of what’s going on down below. The edges of most coins are also crenellated with tiny notches, a design that prevented sneaky people, back when coins were actually made of precious metals, from shaving slivers of gold or silver from their edges. Crenellation is also a culinary technique, as when a baker pinches a pie crust along the edge to form a pleasing pattern. As a word, crenellate has been borrowed twice by English. Most recently, in the mid nineteenth century, crenellate was acquired by adapting the French creneller, meaning to indent. Long before this, however, in the early thirteenth century, the French creneller was borrowed as kernel, meaning indentation, a word that became obsolete in the seventeenth century (the other kernel, the one meaning grain, derives from an unrelated source). Further back in history, the French creneller evolved from the Vulgar Latin crena, meaning notch, which is also the source of the word cranny, as in nook and cranny. In culinary use, a common synonym for crenellate is crimp, a word that emerged in the early eighteenth century. The source of crimp is a Germanic word, pronounced something like kram, that meant to pinch; this Germanic kram is also the source of numerous other “pinching” words, including cramp, cram, clamp, and even clam.