macron

A macron (/ˈmækrɒn, ˈmeɪ-/ MAK-ron, MAY-) is a diacritical mark: it is a straight bar ¯ placed above a letter, usually a vowel. Its name derives from Ancient Greek μακρόν (makrón) 'long' because it was originally used to mark long or heavy syllables in Greco-Roman metrics. It now more often marks a long vowel. In the International Phonetic Alphabet, the macron is used to indicate a mid-tone; the sign for a long vowel is instead a modified triangular colon ⟨ː⟩.

The opposite is the breve ⟨˘⟩, which marks a short or light syllable or a short vowel.