Ksi (Ѯ, ѯ) is a letter of the early Cyrillic alphabet, derived from the Greek letter Xi (Ξ, ξ).^[1] It was mainly used in Greek loanwords, especially words relating to the Church.

Quick Facts Cyrillic letter Ksi, Phonetic usage: ...

Cyrillic letter Ksi
Phonetic usage:	/ks/
Numeric value:	60
Derived from:	Greek letter Xi (Ξ ξ)
The Cyrillic script
Slavic letters
А А̀ А̂ А̄ Ӓ Б В Г Ґ Д Ђ Ѓ Е Ѐ Е̄ Е̂ Ё Є Ж З З́ Ѕ И І Ї Ꙇ Ѝ И̂ Ӣ Й Ј К Л Љ М Н Њ О О̀ О̂ Ō Ӧ П Р Р̌ С С́ Т Ћ Ќ У У̀ У̂ Ӯ Ў Ӱ Ф Х Ц Ч Џ Ш Щ Ꙏ Ъ Ъ̀ Ы Ь Ѣ Э Ю Ю̀ Я 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 Ԑ Ԑ̈ Җ Ӝ Ӂ Ж̣ Ҙ Ӟ З̌ З̣ З̆ 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 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 Ю̄ Я̆ Я̄ Я̈ Ӏ ʼ ˮ
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 Ҧ П̧ П̑ Ҁ Ԛ̆ Р́ Р̀ Р̃ Ԗ С̀ С̈ Ԍ Ҫ̓ Т̓ Т̀ Ԏ Т̑ Ꚋ Т̧ Ꚍ Ꚍ̆ ОУ Ꙋ У̇ У̨ ꙋ́ Ф̑ Ф̓ Х́ Х̀ Х̆ Х̇ Х̧ Х̾ 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
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Unlike other eliminated letters such as omega and yus, Ksi was a later borrowing from Greek and does not appear in any form in the Glagothic script, which was used until the Middle Ages.^[2][3]

Ksi was eliminated from the Russian alphabet along with psi, omega, and yus in the Civil Script of 1708 (Peter the Great's Grazhdanka),^[4] and has also been dropped from other secular languages. It was briefly restored in 1710 and ultimately removed in 1735. While it was no longer used in typographic fonts, it continued to be used by the church, and since clergy actively participated in civil censuses, Ksi can be found in multiple handwritten civil texts all the way until the early 1800s.

In the Civil Script during Peter the Great's time, ksi was also written similarly to an izhitsa with a tail.

Ksi constituted the number "60" in the Cyrillic numeral system.^[5]

• X x : Latin letter X
• Х х : Cyrillic letter Kha
• Ξ ξ : Greek letter Ksi