Definitions:
a tall headdress worn by bishops and senior abbots as a symbol of office, tapering to a point at front and back with a deep cleft between.

a joint made between two pieces of wood or other material at an angle of 90°, such that the line of junction bisects this angle

a mollusc of warm seas which has a sharply pointed shell with a narrow aperture, supposedly resembling a bishop's mitre.

join by means of a mitre joint or seam