Inverted breve

Inverted breve or arch is a diacritical mark, shaped like the top half of a circle ( ̑ ), that is, like an upside-down breve (˘). It looks similar to the circumflex (ˆ), which has a sharp tip (Â â Ê ê Î î Ô ô Û û), while the inverted breve is rounded: (Ȃ ȃ Ȇ ȇ Ȋ ȋ Ȏ ȏ Ȗ ȗ).

Inverted breve can occur above or below the letter. It is not used in any natural language alphabet, but as a phonetic indicator. It is identical in form to the Ancient Greek circumflex.

Serbo-Croatian
The inverted breve above is used in traditional Slavicist notation of Serbo-Croatian phonology to indicate long falling accent. It is placed above the syllable nucleus, which can be one of five vowels (ȃ ȇ ȋ ȏ ȗ) or syllabic ȓ. This use of the inverted breve is derived from the Ancient Greek circumflex, which was preserved in the polytonic orthography of Modern Greek and influenced early Serbian Cyrillic printing through religious literature. In the early 19th century, it began to be used in both Latin and Cyrillic as a diacritic to mark prosody in the systematic study of the Serbo-Croatian linguistic continuum.

International Phonetic Alphabet
In the International Phonetic Alphabet, an inverted breve below is used to mark a vowel as non-syllabic, i.e. assuming the role of a semivowel. The diacritic thus expands upon the four primary symbols the IPA reserves for semivowels, which correspond to the full vowels, respectively. Any vowel is eligible for marking as non-syllabic; a frequent use of the diacritic is in conjunction with the centralised equivalents of the vowels just mentioned:.

The same diacritic is placed under iota (ι̯) to represent the Proto-Indo-European semivowel as it relates to Greek grammar; upsilon with an inverted breve (υ̯) is used alongside digamma (ϝ) to represent the Proto-Indo-European semivowel .

Encoding
Inverted breve characters are supported in Unicode and HTML code (decimal numeric character reference).

In LaTeX the control  with   puts an inverted breve over the letter o.