quoin

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An exterior angle of a wall or other piece of masonry.
• noun 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.
• noun A keystone.
• noun Printing A wedge-shaped block used to lock type in a chase.
• noun A wedge used to raise the level of a gun.
• transitive verb To provide, secure, or raise with a quoin or quoins.

from The Century Dictionary.

• To wedge, steady, or raise with quoins, as a stone in building a wall, the types in a chase, etc.: generally with up. See quoin, n., 2.
• noun The solid angle of a crystal in which three or more faces meet. Also written coign.
• noun An external solid angle; specifically, in architecture and masonry, the external angle of a building.
• noun A wedge-like piece of stone, wood, metal, or other material, used for various purposes.
• noun In gem-cutting, any one of the four facets on the crown of a brilliant; also, any one of the four facets on the pavilion or base. These facets divide each portion of the brilliant into four parts. Also called lozenge. See cut under brilliant.
• noun Nautical, a wedge placed beneath a cask when stowed on shipboard, to prevent it from rolling.
• noun In gunnery, a wooden wedge used to hold a gun at a desired elevation.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Arch.) Originally, a solid exterior angle, as of a building; now, commonly, one of the selected pieces of material by which the corner is marked.
• noun A wedgelike piece of stone, wood, metal, or other material, used for various purposes
• noun (Masonry) To support and steady a stone.
• noun (Gun.) To support the breech of a cannon.
• noun (Print.) To wedge or lock up a form within a chase.
• noun (Naut.) To prevent casks from rolling.
• noun See under Hollow.
• noun (Canals) the post of a lock gate which abuts against the wall.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any of the corner building blocks of a building, usually larger or more ornate than the surrounding blocks.
• noun The keystone of an arch.
• noun 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.
• noun obsolete, nautical A form of wedge used to prevent casks from moving

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun expandable metal or wooden wedge used by printers to lock up a form within a chase
• noun the keystone of an arch
• noun (architecture) solid exterior angle of a building; especially one formed by a cornerstone