(Translated by https://www.hiragana.jp/)
Yat with diaeresis - Wikipedia

Yat with diaeresis (Ѣ̈ ѣ̈) is a letter of the Cyrillic script. It was formerly used in Russian, before 1918 when the yat was removed. The letter comes from a yat with a diaeresis.

Cyrillic letter Yat with diaeresis
The Cyrillic script
Slavic letters
АА̀А̂А̄ӒБВГ
ҐДЂЃЕЀЕ̄Е̂
ЁЄЖЗЗ́ЅИІ
ЇЍИ̂ӢЙЈК
ЛЉМНЊОО̀О̂
ŌӦПРСС́ТЋ
ЌУУ̀У̂ӮЎӰФ
ХЦЧЏШЩЪ
Ъ̀ЫЬѢЭЮЮ̀Я
Я̀
Non-Slavic letters
ӐА̊А̃Ӓ̄ӔӘӘ́Ә̃
ӚВ̌ԜГ̑Г̇Г̣Г̌Г̂
Г̆Г̈г̊ҔҒӺҒ̌
ғ̊ӶД́Д̌Д̈Д̣Д̆
ӖЕ̃Ё̄Є̈ԐԐ̈ҖӜ
ӁЖ̣ҘӞЗ̌З̣З̆Ӡ
И̃ӤҊҚӃҠҞҜ
К̣к̊қ̊ԚЛ́ӅԮ
ԒЛ̈ӍН́ӉҢԨ
ӇҤО̆О̃Ӧ̄ӨӨ̄Ө́
Ө̆ӪԤП̈Р̌ҎР̌С̌
ҪС̣С̱Т́Т̈Т̌Т̇Т̣
ҬУ̃ӲУ̊Ӱ̄ҰҮ
Ү́Х̣Х̱Х̮Х̑Х̌ҲӼ
х̊Ӿӿ̊ҺҺ̈ԦЦ̌Ц̈
ҴҶҶ̣ӴӋҸЧ̇
Ч̣ҼҾШ̣Ы̆Ы̄Ӹ
ҌҨЭ̆Э̄Э̇ӬӬ́
Ӭ̄Ю̆Ю̈Ю̄Я̆Я̄Я̈Ӏ
ʼˮ
Archaic or unused letters
А̨Б̀Б̣Б̱В̀Г̀Г̧
Г̄Г̓Г̆Ҕ̀Ҕ̆ԀД̓
Д̀Д̨ԂЕ̇Е̨
Ж̀Ж̑Џ̆
Ꚅ̆З̀З̑ԄԆ
ԪІ̂І̣І̨
Ј̵Ј̃К̓К̀К̆Ӄ̆
К̑К̇К̈К̄ԞК̂
Л̀ԠԈЛ̑Л̇Ԕ
М̀М̃Н̀Н̄Н̧
Н̃ԊԢН̡Ѻ
П̓П̀
П́ҦП̧П̑ҀԚ̆Р́
Р̀Р̃ԖС̀С̈ԌҪ̓
Т̓Т̀ԎТ̑Т̧
Ꚍ̆ѸУ̇
У̨ꙋ́Ф̑Ф̓Х́Х̀Х̆Х̇
Х̧Х̾Х̓һ̱ѠѼ
ѾЦ̀Ц́Ц̓Ꚏ̆
Ч́Ч̀Ч̆Ч̑Ч̓
ԬꚆ̆Ҽ̆Ш̀
Ш̆Ш̑Щ̆Ꚗ̆Ъ̄Ъ̈
Ъ̈̄Ы̂Ы̃Ѣ́Ѣ̈Ѣ̆
Э̨Э̂Ю̂
Я̈Я̂Я̨ԘѤѦѪ
ѨѬѮѰѲѴ
Ѷ
Cyrillic letter Yat with diaeresis in a dictionary by Vladimir Dal.

It represented instances when yat was pronounced like ё (yo).

See also

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