Definition - A straight horizontal line placed over a vowel to indicate that it is long.

1. Its opposite is the breve, which is used to show that the vowel is short.

Etymology -
The term derives from the Greek macros, long.

Oxford English Dictionary -
Its first citation is from 1851:
"The different uses made of the breve, the macron, and the accents."
(G. Brown Gram. of Gramm. 810 note)

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