MITRE, in Architecture, is the workmen's term for an angle that is just 45 degrees, or half a right one. If the angle be a quarter of a right angle, they call it a half mitre.
To describe such angles, they have an instrument called the mitre square; with this they strike mitre lines on their quarters or battens; and for despatch, they have a mitre bar, as they call it, which is made of two pieces of wood, each about an inch thick, one nailed upright on the edge of the other; the upper piece hath the mitre lines struck upon it on both sides, and a kerf to direct the saw in cutting the mitre joints readily, by only applying the piece into this box.