An external angle or corner of a wall or building; also a cornerstone or quoin, especially in architectural contexts.
From Old French 'coigne', derived from Latin 'cuneus' (wedge), the word described the corner stones used in medieval architecture, later becoming the general term for building angles.
The 'coign of vantage' in Shakespeare's 'Macbeth' refers to a corner position that offers advantage—showing how this architectural term became metaphorical for strategic advantage in general.
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