Meaning

noun joint that forms a corner; usually both sides are bevelled at a 45-degree angle to form a 90-degree corner

noun the surface of a beveled end of a piece where a miter joint is made

noun a liturgical headdress worn by bishops on formal occasions

originFrom Middle English mytre, from Old French mitre, from Ancient Greek μίτρα (mítra, “headband, turban”). Its use in reference to a counterfeit coin derived from the bishop's mitre stamped upon it. Doublet of Mithras, Mithra, Mitra, and Mehr.

Etymology from Wiktionary, CC BY-SA 3.0