quoin also coign or coin 
(koin, kwoin)
(koin, kwoin)n.
1.
a. An exterior angle of a wall or other piece of masonry.
b. Any of the stones used in forming such an angle, often being of large size and dressed or arranged so as to form a decorative contrast with the adjoining walls.
c. A piece of wood or other material used as trim on the corner of a building in imitation of such a stone.
2. A keystone.
3. Printing A wedge-shaped block used to lock type in a chase.
4. A wedge used to raise the level of a gun.
tr.v. quoined, quoin·ing, quoins also coigned or coign·ing or coigns or coined or coin·ing or coins
To provide, secure, or raise with a quoin or quoins.
[Variant of COIN.]
quoinsmooth-cut quoins