Chi (letter)

Chi(/kaɪ/^ⓘKY,also/xiː/KHEE;^[1]^[2]uppercaseΧ,lowercaseχ;Greek:χῖ) is the twenty-second letter of theGreek alphabet.

Greek

The Greek alphabet on ablack figurevessel, with a cross-shaped chi

Pronunciation

Ancient Greek

Its value inAncient Greekwas an aspiratedvelar stop/kʰ/(in theWestern Greek alphabet:/ks/).

Koine Greek

InKoine Greekand later dialects it became africative([x]/[ç]) along withΘandΦ.

Modern Greek

InModern Greek,it has two distinct pronunciations: In front ofhighorfront vowels(/e/or/i/) it is pronounced as avoiceless palatal fricative[ç],as inGermanichor likesome pronunciations of "h"in English words likehewandhuman.In front ofloworback vowels(/a/,/o/or/u/) andconsonants,it is pronounced as avoiceless velar fricative([x]), as in GermanachorSpanishj.This distinction corresponds to the ich-Laut and ach-Laut of German.

Transliteration

Chi isromanizedas⟨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 ofGreek numerals,it has a value of 600.

Xi

In ancient times, somelocal formsof theGreek alphabetused the chi instead ofxito represent the /ks/ sound. This was borrowed into the earlyLatinlanguage, which led to the use of the letter X for the same sound in Latin, and many modern languages that use theLatin alphabet.

Cyrillic

Chi was also included in theCyrillic scriptas the letterХ,with the phonetic value /x/ or /h/.

International Phonetic Alphabet

In theInternational Phonetic Alphabet,⟨ꭓ⟩ represents avoiceless uvular fricative.

Chiasmus

Chi is the basis for the name literarychiastic structureand the name ofchiasmus.

Symbolism

InPlato'sTimaeus,it is explained that the two bands that form thesoul of the worldcross each other like the letter Χ. Plato's analogy, along with several other examples ofchias a symbol occur inThomas Browne's discourseThe Garden of Cyrus(1658).

Chi orXis often used to abbreviate the nameChrist,as in the holidayChristmas(Xmas). When fused within a single typeface with the Greek letterrho,it is called theChi Rhoand used to represent the person of Jesus Christ.

Math and science

Instatistics,the term chi-squared or $\chi ^{2}$ hasvarious uses,including thechi-squared distribution,thechi-squared test,andchi-squared target models.

Inalgebraic topology,Chi is used to represent theEuler characteristicof a surface.

Inneuroanatomy,crossingsofperipheral nerves(such as theoptic chiasm) are named for the letter Chi because of its Χ-shape.^[4]

Inchemistry,themole fraction^[5]^[6]andelectronegativity^[7]may be denoted by the lowercase $\chi$ .

Inphysics, $\chi$ denoteselectricormagnetic susceptibility.

Inrhetoric,bothchiastic structure(aliterary device) and thefigure of speech Chiasmusderive from their names from the shape of the letter Chi.

Inmechanical engineering,chi is used as a symbol for thereduction factorof relevantbucklingloads in theEN 1993,aEuropean Standardfor the design of steel structures.

Ingraph theory,a lowercase chi is used to represent a graph'schromatic number.

Inanalytic number theory,chi is used for theDirichlet character.

Unicode

U+03A7ΧGREEK CAPITAL LETTER CHI(Χ)^[8]
U+03C7χGREEK SMALL LETTER CHI(χ)
U+1D61ᵡMODIFIER LETTER SMALL CHI
U+1D6AᵪGREEK SUBSCRIPT SMALL LETTER CHI
U+2627☧CHI RHO
U+2CACⲬCOPTIC CAPITAL LETTER KHI
U+2CADⲭCOPTIC SMALL LETTER KHI
U+2CE9⳩COPTIC SYMBOL KHI RO
U+A7B3ꞳLATIN CAPITAL LETTER CHI
U+AB53ꭓLATIN SMALL LETTER CHI
U+AB54ꭔLATIN SMALL LETTER CHI WITH LOW RIGHT RING
U+AB55ꭕLATIN SMALL LETTER CHI WITH LOW LEFT SERIF
U+1D6BE𝚾MATHEMATICAL BOLD CAPITAL CHI
U+1D6D8𝛘MATHEMATICAL BOLD SMALL CHI
U+1D6F8𝛸MATHEMATICAL ITALIC CAPITAL CHI
U+1D712𝜒MATHEMATICAL ITALIC SMALL CHI
U+1D732𝜲MATHEMATICAL BOLD ITALIC CAPITAL CHI
U+1D74C𝝌MATHEMATICAL BOLD ITALIC SMALL CHI
U+1D76C𝝬MATHEMATICAL SANS-SERIF BOLD CAPITAL CHI
U+1D786𝞆MATHEMATICAL SANS-SERIF BOLD SMALL CHI
U+1D7A6𝞦MATHEMATICAL SANS-SERIF BOLD ITALIC CAPITAL CHI
U+1D7C0𝟀MATHEMATICAL SANS-SERIF BOLD ITALIC SMALL CHI

References

^"chi".The Chambers Dictionary(9th ed.). Chambers. 2003.ISBN 0-550-10105-5.
^"chi".Oxford English Dictionary(Online ed.).Oxford University Press.(Subscription orparticipating institution membershiprequired.)
^Encyclopædia Britannica
^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
^Unicode Code Charts:Greek and Coptic (Range: 0370-03FF)

[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 orparticipating institution membershiprequired.)

[3] Encyclopædia Britannica

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

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

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

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

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

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