# Chi (letter)

**Chi** /ˈkaɪ/^{[1]} (uppercase **Χ**, lowercase **χ**; Greek: χῖ) is the 22nd 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 the *h* in some pronunciations of the English words *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*.

### Transliteration

Chi is romanized as ⟨ch⟩ in most systematic transliteration conventions, but sometimes ⟨kh⟩ is used.^{[2]} 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, the minuscule chi is the symbol for the 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 typespace with the Greek letter Rho, it is called the labarum and used to represent the person of Jesus Christ.

## Character encodings

### Greek chi

Character | 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 | decimal | hex | decimal | hex | decimal | hex | decimal | 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 |

^{[3]}

### Coptic khi

Character | Ⲭ | ⲭ | ⳩ | |||
---|---|---|---|---|---|---|

Unicode name |
COPTIC CAPITAL LETTER KHI | COPTIC SMALL LETTER KHI | COPTIC SYMBOL KHI RHO | |||

Encodings | decimal | hex | decimal | hex | decimal | 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 | 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 | decimal | hex | decimal | hex | decimal | 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 | 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 | decimal | hex | decimal | hex | decimal | hex | decimal | hex | decimal | 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 | 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 | decimal | hex | decimal | hex | decimal | 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 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.^{[4]}

In chemistry, the mole fraction^{[5]}^{[6]} and electronegativity^{[7]} may be denoted by the lowercase .

In physics, 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.

## See also

Look up or Χ in Wiktionary, the free dictionary.χ |

## References

**^**"chi".*Oxford English Dictionary*(3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library 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 0547125321.**^**Rickard, James N. Spencer, George M. Bodner, Lyman H. (2010).*Chemistry : structure and dynamics*(5th ed.). Hoboken, N.J.: 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