macron

noun

1. a horizontal line used as a diacritic over a vowel to indicate that it has a long sound or other specified pronunciation, as (ā) in fate (fāt).

noun

1. a diacritical mark (¯) placed over a letter, used in prosody, in the orthography of some languages, and in several types of phonetic respelling systems, to represent a long vowel

n.“short horizontal line placed over a vowel to indicate length,” 1827, from Greek makron, neuter of makros “long” (see macro-).