quoin

Short definition from Wiktionary

Noun

1. 1
   Any of the corner building blocks of a building, usually larger or more ornate than the surrounding blocks.
2. 2
   The keystone of an arch.
3. 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. 4
   A form of wedge used to prevent casks from moving.
5. 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.
6. 6
   A number of apple varieties with a distinctive ribbed appearance, like corners of a coin.

Verb

1. 1
   To wedge or steady with quoins.