Ъ

Slavic letters
А Б В Г Ґ Д Ђ Ѓ Е Ѐ Ё Є Ж З Ѕ И Ѝ І Ї Й Ј К Л Љ М Н Њ О П Р С Т Ћ Ќ У Ў Ф Х Ц Ч Џ Ш Щ Ъ Ы Ь Э Ю Я
Non-Slavic letters
Ӑ А̄ А̊ А̃ Ӓ Ӓ̄ Ә Ә́ Ә̃ Ӛ Ӕ Ғ Г̧ Г̑ Г̄ Ҕ Ӻ Ӷ Ԁ Ԃ Ꚃ Ꚁ Ꚉ Ԫ Ԭ С́ Ӗ Е̄ Е̃ Ё̄ Є̈ Ӂ Җ Ꚅ Ӝ Ԅ Ҙ Ӟ З́ Ԑ Ԑ̈ Ӡ Ԇ Ӣ И̃ Ҋ Ӥ Қ Ӄ Ҡ Ҟ Ҝ Ԟ Ԛ Ӆ Ԯ Ԓ Ԡ Ԉ Ԕ Ӎ Ӊ Ң Ԩ Ӈ Ҥ Ԣ Ԋ О̆ О̃ О̄ Ӧ Ө Ө̄ Ӫ Ҩ Ԥ Ҧ Р̌ Ҏ Ԗ Ҫ Ԍ Ꚑ Ҭ Ꚋ Ꚍ Ԏ У̃ Ӯ Ӱ Ӱ́ Ӳ Ү Ү́ Ұ Х̑ Ҳ Ӽ Ӿ Һ Һ̈ Ԧ Ꚕ Ҵ Ꚏ Ҷ Ӵ Ӌ Ҹ Ꚓ Ꚗ Ꚇ Ҽ Ҿ Ы̆ Ы̄ Ӹ Ҍ Э̆ Э̄ Э̇ Ӭ Ӭ́ Ӭ̄ Ю̆ Ю̈ Ю̈́ Ю̄ Я̆ Я̄ Я̈ Ԙ Ԝ Ӏ
Archaic letters
Ꙁ Ꙃ Ꙅ Ꙇ Ꙉ Ҁ Ѻ ОУ Ꙋ Ѡ Ѽ Ꙍ Ѿ Ꙏ Ѣ Ꙑ Ꙓ Ꙕ Ꙗ Ѥ Ѧ Ꙙ Ѫ Ꙛ Ѩ Ꙝ Ѭ Ѯ Ѱ Ѳ Ѵ Ѷ Ꙟ Ꙡ Ꙣ Ꙥ Ꙧ Ꙩ Ꙫ Ꙭ ꙮ Ꚙ Ꚛ
List of Cyrillic letters Cyrillic digraphs

The letter Ъ (italics Ъ, ъ) of the Cyrillic script, also spelled jer or er, is known as the hard sign (твёрдый знак [ˈtvʲɵrdɨj ˈznak]) in the modern Russian and Rusyn alphabets, as er golyam (ер голям, "big er") in the Bulgarian alphabet, and as debelo jer (дебело їер, "fat yer") in pre-reform Serbian orthography. The letter is called back yer or back er in the pre-reform Russian orthography, in Old Russian, and in Old Church Slavonic. Originally the yer denoted an ultra-short or reduced middle rounded vowel. It is one of two reduced vowels that are collectively known as the yers in Slavic philology.

In Modern Russian, the letter "ъ" is called the hard sign (твёрдый знак tvjordyj znak). It has no phonetic value of its own and is purely an orthographic device. Its function is to separate a number of prefixes ending in a consonant from a following morpheme that begins with an iotated vowel. It is therefore commonly seen in front of the letters "я", "е", "ё", and "ю" (ja, je, jo, and ju in Russian). The hard sign marks the fact that the sound [j] continues to be heard in the composition. Example:

It therefore functions as a kind of "separation sign" and has been used only sparingly in the aforementioned cases since the spelling reform of 1918. The consonant before the hard sign often becomes somewhat softened (palatalized) due to the following iotation. As a result, in the twentieth century there were occasional proposals to eliminate the hard sign altogether, and replace it with the soft sign ь, which always marks the softening of a consonant. However, in part because the degree of softening before ъ is not uniform, the proposals were never implemented. The hard sign ъ is written after both native and borrowed prefixes. In recent years, it has sometimes been seen in borrowed words, before the letter и, to mark a greater separation of the constituent syllables. Such written usage has not yet been formally codified (see also Russian phonology and Russian orthography).

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Wikipedia