1.  quoin(n = noun.artifact) coign, coigne - expandable metal or wooden wedge used by printers to lock up a form within a chase;
is a kind of wedge

2.  quoin(n = noun.artifact) coign, coigne - the keystone of an arch;
is a kind of headstone, key, keystone

3.  quoin(n = noun.artifact) corner - (architecture) solid exterior angle of a building; especially one formed by a cornerstone;
is a kind of construction, structure
is a part of building, edifice

1.  Originally, a solid exterior angle, as of a building; now, commonly, one of the selected pieces of material by which the corner is marked. [1913 Webster]
" In stone, the quoins consist of blocks larger than those used in the rest of the building, and cut to dimension. In brickwork, quoins consist of groups or masses of brick laid together, and in a certain imitation of quoins of stone." [1913 Webster]

2.  A wedgelike piece of stone, wood, metal, or other material, used for various purposes; [1913 Webster]

quoin, n. & v.
--n.
1 an external angle of a building.
2 a stone or brick forming an angle; a cornerstone.
3 a wedge used for locking type in a forme.
4 a wedge for raising the level of a gun, keeping the barrel from rolling, etc.
--v.tr. secure or raise with quoins.

Derivative:
quoining n.

Etymology:
var. of COIN