Definition of "mitre"

A covering for the head, worn on solemn occasions by church dignitaries, which has been made in many forms, mostly recently a tall cap with two points or peaks.  examples

The surface forming the bevelled end or edge of a piece where a miter joint is made; also, a joint formed or a junction effected by two beveled ends or edges; a miter joint.  examples

(historical, numismatics) A 13th-century coin minted in Europe which circulated in Ireland as a debased counterfeit sterling penny, outlawed under Edward I.

A cap or cowl for a chimney or ventilation pipe.  examples

A gusset in sewing, etc.  examples

(geometry, rare) A square with one triangular quarter missing from the outside.

A mitre shell  examples

To adorn with a mitre.  examples

To unite at an angle of 45°.  examples