Coign /(koin)/

Coign

n.
  1. 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.
  2. an expandable metal or wooden wedge used by printers to lock up a form within a chase.
  3. the keystone of an arch.