Broad On (Ѻ ѻ; italics: Ѻ ѻ) is a positional and orthographical variant of the Cyrillic letter O (О о) (here "on" (онъ, onŭ) is a traditional name of Cyrillic letter О; these names are still in use in the Church Slavonic alphabet).
Broad On is used only in the Church Slavonic language. In its alphabet (in primers and grammar books), broad and regular shapes of О/о share the same position. Uppercase is typically represented by broad Ѻ, and lowercase is either regular о or dual: both broad ѻ and regular о (in the same way as Greek uppercase Σ is accompanied with two lowercases σ, ς). Phonetically, broad Ѻ/ѻ is the same as regular О/о.
In standard Church Slavonic orthography (since the middle of the 17th century until present time), the broad shape of letter On is used instead of the regular shape of the same letter in the following cases:
- as the first letter of a word's root:
- in the initial position (ѻгнь, ѻтрокъ),
- after a prefix (праѻтецъ),
- in compound words (ѻбоюдуѻстрый),
- in two geographical names (іѻрданъ—Jordan River, іѻппіа—city of Jaffa) and their derivatives,
- as the numerical sign to represent the number 70.
(However, Church Slavonic editions printed outside Russian Empire have often ignored the last rule and used regular о as the numerical sign).
Historically, Broad On was also used in the later Old Russian period, including documents, letters and other vernacular texts, to signal the initial position of a word or a syllable or occasionally to mark a closed vowel (developed in North Russian dialects since the XIV century). It is found in birch bark manuscripts and in some other Russian texts. Other glyphs could be used in the same functions, including Monocular O and Cyrillic Omega.
Broad On has no standard traditional name. The names used in literature (broad/wide/round/initial on/o etc.) are just shape-based or functional descriptions. A name from certain Russian sources, он польское, on pol'skoye (literally, "Polish O"), also points to the round shape of the letter, because Latin fonts from Poland had round "O", and the typical old Cyrillic "O" was lens-shaped and condensed. Now the character is often being referred to by its conventional Unicode name "Round Omega", the fact that may lead to certain misunderstanding, because the Cyrillic letter Omega is a completely different letter; in particular, its numerical value is 800, not 70.
|Unicode name|| CYRILLIC CAPITAL LETTER|
| CYRILLIC SMALL LETTER|
|UTF-8||209 186||D1 BA||209 187||D1 BB|
|Numeric character reference||Ѻ||Ѻ||ѻ||ѻ|
- See, for example: Н. П. Саблина. Буквица славянская. Поэтическая история азбуки с азами церковнославянской грамоты. СПб.: Ижица, 2001. OCLC 51079099 ISBN 978-5-9903415-6-2.
- "Cyrillic: Range: 0400–04FF" (PDF). The Unicode Standard, Version 6.0. 2010. p. 41. Retrieved 2011-06-01.