A symbol (¯) placed over a vowel to show that it has a long sound.
The horizontal mark (¯) used to indicate a stressed or long syllable in a foot of verse.
A short, straight mark (¯) placed over a vowel to indicate that it is long or is to be pronounced in a certain way.
Origin of macron
From the Ancient Greek μακρόν (makron), neuter form of μακρός (makros, “long”) (English macro-).