Chi (letter) - Wikipedia

"χ" and "Χ" redirect here. For the consonant represented by χ in IPA, see Voiceless uvular fricative. "Khi" redirects here. For other uses, see KHI. Not to be confused with X, ×, or Ξ. Twenty-second letter of the Greek alphabet

Chi (/kaɪ/ ⓘ KY, also /xiː/ KHEE;[1][2] uppercase Χ, lowercase χ; Greek: χῖ) is the twenty-second letter of the Greek alphabet.

Greek

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Pronunciation

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Ancient Greek

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Its value in Ancient Greek was an aspirated velar stop /kʰ/ (in the Western Greek alphabet: /ks/).

Koine Greek

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In Koine Greek and later dialects it became a fricative ([x]/[ç]) along with Θ and Φ.

Modern Greek

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In Modern Greek, it has two distinct pronunciations: In front of high or front vowels (/e/ or /i/) it is pronounced as a voiceless palatal fricative [ç], like "h" in English words like hew and human. In front of low or back vowels (/a/, /o/ or /u/) and consonants, it is pronounced as a voiceless velar fricative ([x]), as in German "ch" sound in "Bach" or Spanish j. This is similar to ich-Laut and ach-Laut of German.

Transliteration

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Chi is romanized as ⟨ch⟩ in most systematic transliteration conventions, but sometimes ⟨kh⟩ is used.[3] In addition, in Modern Greek, it is often also romanized as ⟨h⟩ or ⟨x⟩ in informal practice.

Greek numeral

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In the system of Greek numerals, it has a value of 600.

Xi

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In ancient times, some local forms of the Greek alphabet used the chi instead of xi to represent the /ks/ sound. This was borrowed into the early Latin language, which led to the use of the letter X for the same sound in Latin, and many modern languages that use the Latin alphabet.

Cyrillic

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Chi was also included in the Cyrillic script as the letter Х, with the phonetic value /x/ or /h/.

International Phonetic Alphabet

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In the International Phonetic Alphabet, ⟨χ⟩ represents a voiceless uvular fricative.

Chiasmus

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Chi is the basis for the name literary chiastic structure and the name of chiasmus.

Symbolism

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In Plato's Timaeus, it is explained that the two bands that form the soul of the world cross each other like the letter Χ. Plato's analogy, along with several other examples of chi as a symbol occur in Thomas Browne's discourse The Garden of Cyrus (1658).

Chi or X is often used to abbreviate the name Christ, as in the holiday Christmas (Xmas). When fused within a single typeface with the Greek letter rho, it is called the Chi Rho and used to represent the person of Jesus Christ.

Mathematics and science

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• In statistics, the term chi-squared or χ 2 {\displaystyle \chi ^{2}} has various uses, including the chi-squared distribution, the chi-squared test, and chi-squared target model
• In algebraic topology, Chi is used to represent the Euler characteristic of a surface.[4]
• The chromatic number of a graph in graph theory[5]
• In neuroanatomy, crossings of peripheral nerves (such as the optic chiasm) are named for the letter Chi because of its Χ-shape.[6]
• In chemistry, the mole fraction[7][8] and electronegativity[9] may be denoted by the lowercase χ {\displaystyle \chi } .
• In physics, χ {\displaystyle \chi } denotes electric or magnetic susceptibility.[10][11]
• In rhetoric, both chiastic structure (a literary device) and the figure of speech Chiasmus derive from their names from the shape of the letter Chi.
• In mechanical engineering, chi is used as a symbol for the reduction factor of relevant buckling loads in the EN 1993, a European Standard for the design of steel structures.
• In analytic number theory, chi is used for the Dirichlet character.

Unicode

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• U+03A7 Χ GREEK CAPITAL LETTER CHI (Χ)[12]
• U+03C7 χ GREEK SMALL LETTER CHI (χ)
• U+1D61 ᵡ MODIFIER LETTER SMALL CHI
• U+1D6A ᵪ GREEK SUBSCRIPT SMALL LETTER CHI
• U+2627 ☧ CHI RHO
• U+2CAC Ⲭ COPTIC CAPITAL LETTER KHI
• U+2CAD ⲭ COPTIC SMALL LETTER KHI
• U+2CE9 ⳩ COPTIC SYMBOL KHI RO
• U+A7B3 Ꭓ LATIN CAPITAL LETTER CHI
• U+AB53 ꭓ LATIN SMALL LETTER CHI
• U+AB54 ꭔ LATIN SMALL LETTER CHI WITH LOW RIGHT RING
• U+AB55 ꭕ LATIN SMALL LETTER CHI WITH LOW LEFT SERIF
• U+1D6BE 𝚾 MATHEMATICAL BOLD CAPITAL CHI
• U+1D6D8 𝛘 MATHEMATICAL BOLD SMALL CHI
• U+1D6F8 𝛸 MATHEMATICAL ITALIC CAPITAL CHI
• U+1D712 𝜒 MATHEMATICAL ITALIC SMALL CHI
• U+1D732 𝜲 MATHEMATICAL BOLD ITALIC CAPITAL CHI
• U+1D74C 𝝌 MATHEMATICAL BOLD ITALIC SMALL CHI
• U+1D76C 𝝬 MATHEMATICAL SANS-SERIF BOLD CAPITAL CHI
• U+1D786 𝞆 MATHEMATICAL SANS-SERIF BOLD SMALL CHI
• U+1D7A6 𝞦 MATHEMATICAL SANS-SERIF BOLD ITALIC CAPITAL CHI
• U+1D7C0 𝟀 MATHEMATICAL SANS-SERIF BOLD ITALIC SMALL CHI

See also

[edit] Look up Χ or χ in Wiktionary, the free dictionary.

• Chi (disambiguation)
• Х, х - Kha (Cyrillic)

References

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1. ^ "chi". The Chambers Dictionary (9th ed.). Chambers. 2003. ISBN 0-550-10105-5.
2. ^ "chi". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
3. ^ "Greek language | Definition, Alphabet, Origin, & Facts | Britannica". www.britannica.com. 2024-12-20. Retrieved 2025-02-09. Some differences in transliteration result from changes in pronunciation of the Greek language; others reflect convention, as for example the χ (chi or khi), which was transliterated by the Romans as ch (because they lacked the letter k in their usual alphabet). In Modern Greek, however, the standard transliteration for χ is kh.
4. ^ Weisstein, Eric W. "Euler Characteristic". mathworld.wolfram.com. Retrieved 2025-02-09.
5. ^ Weisstein, Eric W. "Chromatic Number". mathworld.wolfram.com. Retrieved 2025-02-09. The chromatic number of a graph G is most commonly denoted χ (G) (e.g., Skiena 1990, West 2000, Godsil and Royle 2001, Pemmaraju and Skiena 2003),...
6. ^ Asimov, Isaac (1963). The Human Brain. Boston: Houghton Mifflin.
7. ^ Zumdahl, Steven S. (2008). Chemistry (8th ed.). Cengage Learning. p. 201. ISBN 978-0-547-12532-9.
8. ^ Spencer, James N.; Bodner, George M.; Rickard, Lyman H. (2010). Chemistry: structure and dynamics (5th ed.). Hoboken, New Jersey: Wiley. p. 357. ISBN 978-0-470-58711-9.
9. ^ IUPAC, Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (2006–) "Electronegativity". doi:10.1351/goldbook.E01990
10. ^ Mugiraneza, Sam; Hallas, Alannah M. (2022-04-19). "Tutorial: a beginner's guide to interpreting magnetic susceptibility data with the Curie-Weiss law". Communications Physics. 5 (1): 1–12. arXiv:2205.07107. doi:10.1038/s42005-022-00853-y. ISSN 2399-3650. However, for newly synthesized materials, there is one indispensable characterization technique that is as old as the field of magnetism itself: magnetic susceptibility, χ,...
11. ^ Jiles, David (2016). Introduction to magnetism and magnetic materials (Third ed.). Boca Raton London New York: CRC Press, Taylor & Francis Group. p. 42. ISBN 978-1-138-44149-1. We can now make a general statement for the permeability μ and susceptibility χ
12. ^ Unicode Code Charts: Greek and Coptic (Range: 0370-03FF)