quoin

1. Any of the corner building blocks of a building, usually larger or more ornate than the surrounding blocks.
2. The keystone of an arch.
3. 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.
4. A form of wedge used to prevent casks from moving
5. 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.

verb

To wedge or steady with quoins.