coign of vantage a favourable position for observation or action. literary

☞ The literal sense of a coign of vantage is 'a projecting corner of a wall or building'; the phrase appears in Shakespeare's Macbeth in Duncan's description of the nesting places of the swifts at Macbeth's castle. The word quoin meaning 'an external angle of a building' still exists in English, but the archaic spelling coign survives mainly in this phrase.