1) Coigne 2) Quoin 3) The keystone of an arch 4) Wall angle 5) Wedge 1) Coigne 2) Quoin 
angle; viewpoint
• (n.) A var. spelling of Coin, Quoin, a corner, wedge; -- chiefly used in the phrase coign of vantage, a position advantageous for action or observation.
Coign noun A var. spelling of Coin , Quoin , a corner, wedge; -- chiefly used in the phrase coign of vantage , a position advantageous for action or observation. « From some shielded nook or coign of vantage.» The Century. « The lithosphere would...