one of the usually differentiated blocks or stones that form the solid exterior angle of a building; also the exterior angle itself
About the Word:
Quoin is an alteration of coin, a word whose Anglo-French ancestor meant "wedge" or "corner." Architecture is rich in styles of quoins, but most quoins are toothed and set in a regular pattern of alternating lengths. They're both decorative and structural, since they usually differ in jointing, color, texture, or size from the masonry of the adjoining walls.