*quoin*

n. [ See Coin, and cf. Coigne. ] 1. (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. [ 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; as: (a) (Masonry) To support and steady a stone. (b) (Gun.) To support the breech of a cannon. (c) (Print.) To wedge or lock up a form within a chase. (d) (Naut.) To prevent casks from rolling. [ 1913 Webster ]

Hollow quoin. See under Hollow. --
Quoin post (Canals), the post of a lock gate which abuts against the wall. [ 1913 Webster ]