Macron (diacritic)

A macron (/ˈmækrɒn, ˈm-/) 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", since 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.

̄
Macron (diacritic)
Diacritics in Latin & Greek
accent
acute´
double acute˝
grave`
double grave ̏
circumflexˆ
caron, háčekˇ
breve˘
inverted breve  ̑  
cedilla¸
diaeresis, umlaut¨
dot·
palatal hook  ̡
retroflex hook  ̢
hook above ̉
horn ̛
iota subscript ͅ 
macronˉ
ogonek, nosinė˛
perispomene ͂ 
overring˚
underring˳
rough breathing
smooth breathing᾿
Marks sometimes used as diacritics
apostrophe
bar◌̸
colon:
comma,
full stop/period.
hyphen˗
prime
tilde~
Diacritical marks in other scripts
Arabic diacritics
Early Cyrillic diacritics
kamora ҄
pokrytie ҇
titlo ҃
Hebrew diacritics
Indic diacritics
anusvara
avagraha
chandrabindu
nuqta
virama
visarga
Gurmukhī diacritics
Khmer diacritics
Thai diacritics
IPA diacritics
Japanese kana diacritics
dakuten
handakuten
Syriac diacritics
Related
Dotted circle
Punctuation marks
Logic symbols
Latin
Āā
Ā́ā́
Ā̀ā̀
Ā̂ā̂
Ā̃ā̃
Ǟǟ
Ā̈ā̈
Ǡǡ
Å̄å̄
Ǣǣ
Ēē
Ē̂ē̂
Ē̃ē̃
Ê̄ê̄
Ë̄ë̄
E̊̄e̊̄
Īī
Ī́ī́
Ī̀ī̀
Ī̂ī̂
Ī̃ī̃
Ōō
Ō̂ō̂
Ō̃ō̃
Ȫȫ
Ō̈ō̈
Ǭǭ
Ȭȭ
Ȱȱ
Ø̄ø̄
Œ̄œ̄
Ūū
Ū́ū́
Ū̀ū̀
Ū̂ū̂
Ū̃ū̃
U̇̄u̇̄
Ǖǖ
Ṳ̄ṳ̄
Ȳȳ
Ȳ́ȳ́
Ȳ̀ȳ̀
Ȳ̃ȳ̃
Greek
Ēɛ̄
Cyrillic
А̄а̄
Ӣӣ
Ӯӯ

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