quoin

Any of the corner building blocks of a building, usually larger or more ornate than the surrounding blocks.

The keystone of an arch.

(printing, historical) A metal wedge which fits into the space between the type and the edge of a chase, and is tightened to fix the metal type in place.

(obsolete, nautical) A form of wedge used to prevent casks from moving

(firearms) A wedge of wood or iron put under the breech of heavy guns or the muzzle of siege-mortars to raise them to the proper level.

(horticulture) A number of apple varieties with a distinctive ribbed appearance, like corners of a coin.