In architecture, both the external corner of a building and, more often, one of the stones used to form that corner. These stones are both structural and decorative in that they often differ in jointing, colour, texture, or size from the masonry of the adjoining walls. Usually quoins are toothed (i.e., set in short courses in a regular pattern of alternating lengths). Such construction dates back to ancient Rome
Wedge set beneath the breech of a gun and moved in or out to adjust elevation It was eventually superseded by the elevating screw Sometimes spelled coin in contemporary works
One of the corner stones of an exterior façade when these are emphasized by size, by more formal cutting, by more conspicuous jointing or by difference in texture