What does "coign" mean?

Coign: 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 be depressed on four faces; . . . the four projecting coigns would stand up as continents. Nature.