mitre

Mitre comes from Greek μίτρα, mitra, a word for a headband, belt, or turban-like wrap. Greek used it for a strip of cloth tied around the body or head, not for a bishop's tall ceremonial headdress. The object was flexible and practical at first. Rank came later.

Latin borrowed the word as mitra, keeping the sense of a headband or oriental-style head covering. In late antique and medieval church usage, the term narrowed onto the ceremonial headdress worn by bishops and certain abbots. By the 11th century, the mitre was a clear sign of ecclesiastical office in the Latin West. The cloth band had become an emblem.

Old French passed it on as mitre, and Middle English adopted the same form. English spelling stabilized as mitre in British usage, while miter became the common American spelling. The word also developed technical senses in carpentry and geometry because joined edges meet like the peaked lines of the headdress. A church garment gave its shape to a tool term.

Today mitre usually means the ceremonial headpiece of a bishop, or by extension a sharply angled joint. The religious sense remains the historical center. The older Greek sense survives mostly in dictionaries and etymology. It is a band that rose into office.