Chi (letter)

Chi (/ˈkaɪ, ˈxiː/ ^ⓘ;^[1]^[2] uppercase Χ, lowercase χ; Greek: χῖ) is the twenty-second letter of the Greek alphabet.

Greek

Pronunciation

Ancient Greek

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

Koine Greek

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

Modern Greek

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], as in German ich or like some pronunciations of "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 ach or Spanish j. This distinction corresponds to the ich-Laut and ach-Laut of German.

Transliteration

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

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

Xi

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

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

International Phonetic Alphabet

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

Chiasmus

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

Symbolism

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.

Character encodings

Greek chi

Character information
Preview	Χ		χ		ᵡ		ᵪ		☧
Unicode name	GREEK CAPITAL LETTER CHI		GREEK SMALL LETTER CHI		MODIFIER LETTER SMALL CHI		GREEK SUBSCRIPT SMALL LETTER CHI		CHI RHO
Encodings	decimal	hex	dec	hex	dec	hex	dec	hex	dec	hex
Unicode	935	U+03A7	967	U+03C7	7521	U+1D61	7530	U+1D6A	9767	U+2627
UTF-8	206 167	CE A7	207 135	CF 87	225 181 161	E1 B5 A1	225 181 170	E1 B5 AA	226 152 167	E2 98 A7
Numeric character reference	Χ	Χ	χ	χ	ᵡ	ᵡ	ᵪ	ᵪ	☧	☧
Named character reference	Χ		χ
DOS Greek	148	94	173	AD
DOS Greek-2	210	D2	243	F3
Windows 1253	214	D6	246	F6
TeX			\chi

^[4]

Coptic khi

Character information
Preview	Ⲭ		ⲭ		⳩
Unicode name	COPTIC CAPITAL LETTER KHI		COPTIC SMALL LETTER KHI		COPTIC SYMBOL KHI RHO
Encodings	decimal	hex	dec	hex	dec	hex
Unicode	11436	U+2CAC	11437	U+2CAD	11497	U+2CE9
UTF-8	226 178 172	E2 B2 AC	226 178 173	E2 B2 AD	226 179 169	E2 B3 A9
Numeric character reference	Ⲭ	Ⲭ	ⲭ	ⲭ	⳩	⳩

Latin chi

Character information
Preview	Ꭓ		ꭓ		ꭔ		ꭕ
Unicode name	LATIN CAPITAL LETTER CHI		LATIN SMALL LETTER CHI		LATIN SMALL LETTER CHI WITH LOW RIGHT RING		LATIN SMALL LETTER CHI WITH LOW LEFT SERIF
Encodings	decimal	hex	dec	hex	dec	hex	dec	hex
Unicode	42931	U+A7B3	43859	U+AB53	43860	U+AB54	43861	U+AB55
UTF-8	234 158 179	EA 9E B3	234 173 147	EA AD 93	234 173 148	EA AD 94	234 173 149	EA AD 95
Numeric character reference	Ꭓ	Ꭓ	ꭓ	ꭓ	ꭔ	ꭔ	ꭕ	ꭕ

Mathematical chi

Character information
Preview	𝚾		𝛘		𝛸		𝜒		𝜲		𝝌
Unicode name	MATHEMATICAL BOLD CAPITAL CHI		MATHEMATICAL BOLD SMALL CHI		MATHEMATICAL ITALIC CAPITAL CHI		MATHEMATICAL ITALIC SMALL CHI		MATHEMATICAL BOLD ITALIC CAPITAL CHI		MATHEMATICAL BOLD ITALIC SMALL CHI
Encodings	decimal	hex	dec	hex	dec	hex	dec	hex	dec	hex	dec	hex
Unicode	120510	U+1D6BE	120536	U+1D6D8	120568	U+1D6F8	120594	U+1D712	120626	U+1D732	120652	U+1D74C
UTF-8	240 157 154 190	F0 9D 9A BE	240 157 155 152	F0 9D 9B 98	240 157 155 184	F0 9D 9B B8	240 157 156 146	F0 9D 9C 92	240 157 156 178	F0 9D 9C B2	240 157 157 140	F0 9D 9D 8C
UTF-16	55349 57022	D835 DEBE	55349 57048	D835 DED8	55349 57080	D835 DEF8	55349 57106	D835 DF12	55349 57138	D835 DF32	55349 57164	D835 DF4C
Numeric character reference	𝚾	𝚾	𝛘	𝛘	𝛸	𝛸	𝜒	𝜒	𝜲	𝜲	𝝌	𝝌

Character information
Preview	𝝬		𝞆		𝞦		𝟀
Unicode name	MATHEMATICAL SANS-SERIF BOLD CAPITAL CHI		MATHEMATICAL SANS-SERIF BOLD SMALL CHI		MATHEMATICAL SANS-SERIF BOLD ITALIC CAPITAL CHI		MATHEMATICAL SANS-SERIF BOLD ITALIC SMALL CHI
Encodings	decimal	hex	dec	hex	dec	hex	dec	hex
Unicode	120684	U+1D76C	120710	U+1D786	120742	U+1D7A6	120768	U+1D7C0
UTF-8	240 157 157 172	F0 9D 9D AC	240 157 158 134	F0 9D 9E 86	240 157 158 166	F0 9D 9E A6	240 157 159 128	F0 9D 9F 80
UTF-16	55349 57196	D835 DF6C	55349 57222	D835 DF86	55349 57254	D835 DFA6	55349 57280	D835 DFC0
Numeric character reference	𝝬	𝝬	𝞆	𝞆	𝞦	𝞦	𝟀	𝟀

These characters are used only as mathematical symbols. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style.

Math and science

In statistics, the term chi-squared or $\chi ^{2}$ has various uses, including the chi-squared distribution, the chi-squared test, and chi-squared target models.

In algebraic topology, Chi is used to represent the Euler characteristic of a surface.

In neuroanatomy, crossings of peripheral nerves (such as the optic chiasm) are named for the letter Chi because of its Χ-shape.^[5]

In chemistry, the mole fraction^[6]^[7] and electronegativity^[8] may be denoted by the lowercase $\chi$ .

In physics, $\chi$ denotes electric or magnetic susceptibility.

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 graph theory, a lowercase chi is used to represent a graph's chromatic number.

In analytic number theory, chi is used for the Dirichlet character.

References

^ "chi". The Chambers Dictionary (9th ed.). Chambers. 2003. ISBN 0-550-10105-5.
^ "chi". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^ Encyclopædia Britannica
^ Unicode Code Charts: Greek and Coptic (Range: 0370-03FF)
^ Asimov, Isaac (1963). The Human Brain. Boston: Houghton Mifflin.
^ Zumdahl, Steven S. (2008). Chemistry (8th ed.). Cengage Learning. p. 201. ISBN 978-0547125329.
^ Spencer, James N.; Bodner, George M.; Rickard, Lyman H. (2010). Chemistry: structure and dynamics (5th ed.). Hoboken, NJ: Wiley. p. 357. ISBN 9780470587119.
^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "Electronegativity". doi:10.1351/goldbook.E01990

[Chambers-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] Encyclopædia Britannica

[4] Unicode Code Charts: Greek and Coptic (Range: 0370-03FF)

[5] Asimov, Isaac (1963). The Human Brain. Boston: Houghton Mifflin.

[6] Zumdahl, Steven S. (2008). Chemistry (8th ed.). Cengage Learning. p. 201. ISBN 978-0547125329.

[7] Spencer, James N.; Bodner, George M.; Rickard, Lyman H. (2010). Chemistry: structure and dynamics (5th ed.). Hoboken, NJ: Wiley. p. 357. ISBN 9780470587119.

[8] IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "Electronegativity". doi:10.1351/goldbook.E01990

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