- the external corner of a building; esp., any of the large, squared stones by which the corner of a building is marked
- a wedgelike piece of stone, etc., such as the keystone or one of the pieces of an arch
- a wedge-shaped wooden or metal block used to lock up type in a galley or form, to keep casks from rolling, etc.
Origin of quoinvariant, variety of coin
- to secure with a quoin
- to furnish with quoins, or corners