noun (n)

• expandable metal or wooden wedge used by printers to lock up a form within a chase(noun.artifact)

  Synonym:
  coigne, quoin
  

  source: wordnet30
• the keystone of an arch(noun.artifact)

  source: wordnet30
• A var. spelling of Coin, Quoin, a corner, wedge; -- chiefly used in the phrase coign of vantage, a position advantageous for action or observation.(noun)

  source: webster1913