Macrons

A macron, from Greek μακρόv (makrón) meaning "long", is a diacritic placed over or under a vowel, originally used to mark a long (i.e., heavy) syllable in Græco-Roman metrics, but now also indicates that the vowel is long. (The opposite is a breve ˘, used to indicate originally a short syllable and now also a short vowel.) Distinctions between long and short vowels are usually phonemic. In the International Phonetic Alphabet the macron is used to indicate mid tone; the sign for a long vowel is a modified triangular colon.

Syllable weight

In Græco-Roman metrics and in the description of the metrics of other literatures, the macron was introduced and is still widely used to mark a long (i.e., heavy) syllable. Even the best and relatively recent classical Greek and Latin dictionaries are still only concerned with indicating the length (i.e., weight) of syllables; that is why most still do not indicate the length of vowels in syllables that are otherwise metrically determined. Though many ancient Roman and Greek textbooks employ the macron, it was not used in ancient Rome or Greece. The macron is to make reading a word easier.

Vowel length

The following languages or transliteration systems use the macron to mark long vowels:

Slavicists use the macron to indicate a non-tonic long vowel, or a non-tonic syllabic liquid, such as on l, lj, m, n, nj, and r. Languages with this feature include standard and jargon varieties of Serbian, Croatian, Macedonian, Czech, Slovak, Bulgarian.
Transcriptions of Arabic typically use macrons to indicate long vowels — ا (alif when pronounced as /aː/), و (waw, when pronounced as /uː/), and ي (ya', when pronounced as /iː/). Thus the Arabic word ثلاثة (three) is transliterated ṯalāṯah.
Some modern dictionaries of classical Greek and Latin, where the macron is sometimes used in conjunction with the breve. However, many such dictionaries still have ambiguities in their treatment and distinction of long vowels or heavy syllables.
The Hepburn romanization system of Japanese. Examples: kōtsū (交通) "traffic" as opposed to kotsu (骨) "bone" or "knack" (fig.)
Latvian. "Ā", "ē", "ī", "ū" are separate letters that sort in alphabetical order immediately after "a", "e", "i", "u" respectively.
Lithuanian. "Ū" is a separate letter but given the same position in collation as the unaccented "u". It marks a long vowel; other long vowels are indicated with an ogonek (which used to indicate nasalization, but no longer does): "ą", "ę", "į", "ų", "o" being always long in Lithuanian except for some recent loanwords. For the long counterpart of "i", "y" is used.
Transcriptions of Nahuatl (spoken in Mexico). Since Nahuatl (Nāhuatl) (Aztecs' language) did not have a writing system, when Spanish conquistadors arrived, they wrote the language in their own alphabet without distinguishing long vowels. Over a century later, in 1645, Horacio Carochi defined macrons to mark long vowels ā, ē, ī and ō, and short vowels with grave (`) accents. This is rare nowadays since many people write Nahuatl without any orthographic sign and with the letters /k/, /s/ and /w/, not present in the original alphabet. Some projects prefer macron-based writing, as in Nahuatl Wikipedia.
Modern transcriptions of Old English.
Latin transliteration of Pali and Sanskrit.
Polynesian languages:
- Hawaiian. The macron is called kahakō, and it indicates vowel length, which changes meaning and the placement of stress.
- Māori. Early writing in Māori did not distinguish vowel length. Some — notably the late Professor Bruce Biggs — have advocated that double vowels be written to mark long vowel sounds (e.g., Maaori), but he was more concerned that they be marked at all than with the method. The Māori Language Commission (Te Taura Whiri o te Reo Māori) advocates that macrons be used to designate long vowels. The use of the macron is widespread in modern Māori, although sometimes the diaeresis mark is used instead (eg. "Mäori" instead of "Māori") if the macron is not available for technical reasons[1]. The Māori words for macron are pōtae "hat", or tohuto.
- Tongan. Called the toloi, its usage is similar to that in Māori, including its substitution by a diaeresis.

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