quoin / k(w)oin/ • n. 1. an external angle of a wall or building. ∎  (also quoin stone) any of the stones or bricks forming such an angle; a cornerstone. 2. Printing a wedge or expanding mechanical device used for locking a letterpress form into a chase. 3. a wedge for raising the level of a gun barrel or for keeping it from rolling.• v. [tr.] 1. provide (a wall) with quoins or corners. 2. Printing lock up (a form) with a quoin.

quoin (also coign, coin, coyn).
1. Any external angle or corner of a structure.

2. Angular courses of stone, etc., at the corner of a building, usually laid as alternate quoin headers and quoin stretchers, often dressed with channels around them so they project from the naked of the wall (rustic quoins).

3. One of the dressed stones used to dress and strengthen the corner of a building. See also long-and-short work.

quoin external angle of a wall or building, corner-stone; wedge, wedge-shaped block. XVI. var. of COIN.