Multiocular O

Multiocular O (ꙮ) is a rare glyph variant of the Cyrillic letter O. This glyph variant can be found in a single 15th century manuscript, in the Old Church Slavonic phrase "серафими многоꙮчитїй" (abbreviated "мн҇оꙮчитїй") (serafimi mnogoočitii, "many-eyed seraphim"). It was documented by Yefim Karsky[1] in 1928 in a copy of the Book of Psalms[2] (back of page 244) from around 1429, now found in the collection[3] of the Trinity Lavra of St. Sergius.

Cyrillic letter Multiocular O
The Cyrillic script
Slavic letters
А А́ А̀ А̂ А̄ Ӓ Б В Г Ґ Д Ђ Ѓ Е Е́ Ѐ Е̄ Е̂ Ё Є Є́ Ж З З́ Ѕ И І І́ Ї Ї́ Ꙇ И́ Ѝ И̂ Ӣ Й Ј К Л Љ М Н Њ О О́ О̀ О̂ Ō Ӧ П Р С С́ Т Ћ Ќ У У́ У̀ У̂ Ӯ Ў Ӱ Ф Х Ц Ч Џ Ш Щ Ꙏ Ъ Ъ̀ Ы Ы́ Ь Ѣ Э Э́ Ю Ю́ Ю̀ Я Я́ Я̀
Non-Slavic letters
Ӑ А̊ А̃ Ӓ̄ Ӕ Ә Ә́ Ә̃ Ӛ В̌ Ԝ Г̑ Г̇ Г̣ Г̌ Г̂ Г̆ Г̈ Ҕ Ғ Ӻ Ғ̌ Ӷ Д́ Д̌ Д̈ Д̣ Д̆ Ӗ Е̃ Ё̄ Є̈ Җ Ӝ Ӂ Ж̣ Ҙ Ӟ З̌ З̣ З̆ Ԑ Ԑ̈ Ӡ И̃ Ӥ Ҋ Қ Ӄ Ҡ Ҟ Ҝ К̣ Ԛ ᴫ Л́ Ӆ Ԯ Ԓ Л̈ Ӎ ᵸ Н́ Ӊ Ң Ԩ Ӈ Ҥ О̆ О̃ Ӧ̄ Ө Ө̄ Ө́ Ө̆ Ӫ Ԥ П̈ Р̌ Ҏ С̌ Ҫ С̣ С̱ Т́ Т̈ Т̌ Т̇ Т̣ Ҭ У̃ Ӳ У̊ Ӱ̄ Ұ Ү Ү́ Х̣ Х̱ Х̮ Х̑ Х̌ Ҳ Ӽ Ӿ Һ Һ̈ Ԧ Ц̌ Ц̈ Ҵ Ҷ Ҷ̣ Ӵ Ӌ Ҹ Ч̇ Ч̣ Ҽ Ҿ Ш̈ Ш̣ ꚜ Ы̆ Ы̄ Ӹ ꚝ Ҍ Ҩ Э̆ Э̄ Э̇ Ӭ Ӭ́ Ӭ̄ Ю̆ Ю̈ Ю̈́ Ю̄ Я̆ Я̄ Я̈ Я̈́ Ӏ
Archaic or unused letters
А̨ Б̀ Б̣ Б̱ В̀ Г̀ Г̧ Г̄ Г̓ Г̆ Ҕ̀ Ҕ̆ Ԁ Д̓ Д̀ Д̨ Ԃ Ꚁ Ꙣ Е̇ Е̨ Ж̀ Ж̑ Ꙃ Ꙅ Џ̆ Ꚅ Ꚅ̆ Ꙁ З̀ З̑ Ԅ Ԇ Ꚉ Ԫ Ꚃ Ꚕ І̂ І̣ І̨ Ј̵ Ј̃ Ꙉ К̓ К̀ К̆ Ӄ̆ К̑ К̇ К̈ К̄ Ԟ К̂ Л̀ Ԡ Ꙥ Ԉ Л̑ Л̇ Ԕ М̀ М̃ Ꙧ Н̀ Н̄ Н̧ Н̃ Ԋ Ԣ Н̡ Ѻ Ꙩ Ꙫ Ꙭ ꙮ Ꚙ Ꚛ П̓ П̀ П́ П̧ Ҧ П̑ Ҁ Ԛ̆ Р́ Р̀ Р̃ Ԗ С̀ С̈ Ԍ Ҫ̓ Т̓ Т̀ Ԏ Т̑ Ꚋ Т̧ Ꚍ Ꚍ̆ Ѹ Ꙋ У̇ У̨ ꙋ́ Ф̑ Ф̓ Х́ Х̀ Х̆ Х̇ Х̧ Х̓ һ̱ Ѡ Ꙍ Ѽ Ѿ Ꙡ Ц̀ Ц́ Ц̓ Ꚏ Ꚏ̆ Ꚑ Ч́ Ч̀ Ч̆ Ч̑ Ч̓ Ԭ Ꚓ Ꚇ Ꚇ̆ Ҽ̆ Ш̀ Ш̆ Ш̑ Щ̆ Ꚗ Ꚗ̆ Ꙑ Ы̂ Ы̃ Ѣ́ Ѣ̈ Ѣ̆ Ꙓ Э̨ Э̂ Ꙕ Ю̂ Ꙗ Я̈ Я̂ Я̨ Ԙ Ѥ Ѧ Ꙙ Ѫ Ꙛ Ѩ Ꙝ Ѭ Ѯ Ѱ Ѳ Ѵ Ѷ Ꙟ
List of Cyrillic letters List of Cyrillic multigraphs

There's a very likely chance that Multiocular O was a result of a writer’s attempt at depicting how many eyes the seraphim they were describing had.

The character was proposed for inclusion into Unicode in 2007[4] and incorporated as character U+A66E in Unicode version 5.1 (2008).[5] The representative glyph had seven eyes. However, in 2021, following a tweet highlighting the character,[6] it came to linguist Michael Everson's attention that the character in the 1429 manuscript was actually made up of ten eyes. After a 2022 proposal to change the character to reflect this, it was updated later that year for Unicode 15.0 to have ten eyes.[7][8]

The letter in the original manuscript.

The incorrect form originally implemented into Unicode (2007–2022).