Xi (letter)

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Not to be confused with "≡", the triple bar character.

Xi (uppercase Ξ, lowercase ξ; Greek: ξι) is the 14th letter of the Greek alphabet. It is pronounced [ksi] in Modern Greek, and generally /ˈz/ or /ˈs/ in English.[1] In the system of Greek numerals, it has a value of 60. Xi was derived from the Phoenician letter samekh Phoenician samekh.svg.

Xi is not to be confused with the letter chi, which gave its form to the Latin letter X.

Greek[edit]

A joined variant of Ξ.

Both in classical Ancient Greek and in Modern Greek, the letter Ξ represents the sound [ks]. In some archaic local variants of the Greek alphabet, this letter was missing. Instead, especially in the dialects of most of the Greek mainland and Euboea, the sound [ks] was represented by Χ (which in classical Greek is chi, used for /kʰ/). Because this variant of the Greek alphabet was used in Italy, the Latin alphabet borrowed Χ rather than Ξ as the Latin letter X.

Cyrillic[edit]

While having no Latin derivative, the Xi was adopted into the early Cyrillic alphabet, as the letter ksi (Ѯ, ѯ).

Mathematics and science[edit]

Upper case[edit]

The upper-case letter Ξ is used as symbol for:

Lower case[edit]

The lower-case letter ξ is used as a symbol for:

Character Encodings[edit]

  • Greek Xi / Coptic Ksi
Character Ξ ξ
Unicode name GREEK CAPITAL LETTER XI GREEK SMALL LETTER XI COPTIC CAPITAL LETTER KSI COPTIC SMALL LETTER KSI
Encodings decimal hex decimal hex decimal hex decimal hex
Unicode 926 U+039E 958 U+03BE 11420 U+2C9C 11421 U+2C9D
UTF-8 206 158 CE 9E 206 190 CE BE 226 178 156 E2 B2 9C 226 178 157 E2 B2 9D
Numeric character reference Ξ Ξ ξ ξ Ⲝ Ⲝ ⲝ ⲝ
Named character reference Ξ ξ
DOS Greek 141 8D 165 A5
DOS Greek-2 189 BD 232 E8
Windows 1253 206 CE 238 EE
TeX \Xi \xi

[3]

  • Mathematical Xi
Character 𝚵 𝛏 𝛯 𝜉 𝜩 𝝃
Unicode name MATHEMATICAL BOLD
CAPITAL XI
MATHEMATICAL BOLD
SMALL XI
MATHEMATICAL ITALIC
CAPITAL XI
MATHEMATICAL ITALIC
SMALL XI
MATHEMATICAL BOLD ITALIC
CAPITAL XI
MATHEMATICAL BOLD ITALIC
SMALL XI
Encodings decimal hex decimal hex decimal hex decimal hex decimal hex decimal hex
Unicode 120501 U+1D6B5 120527 U+1D6CF 120559 U+1D6EF 120585 U+1D709 120617 U+1D729 120643 U+1D743
UTF-8 240 157 154 181 F0 9D 9A B5 240 157 155 143 F0 9D 9B 8F 240 157 155 175 F0 9D 9B AF 240 157 156 137 F0 9D 9C 89 240 157 156 169 F0 9D 9C A9 240 157 157 131 F0 9D 9D 83
UTF-16 55349 57013 D835 DEB5 55349 57039 D835 DECF 55349 57071 D835 DEEF 55349 57097 D835 DF09 55349 57129 D835 DF29 55349 57155 D835 DF43
Numeric character reference 𝚵 𝚵 𝛏 𝛏 𝛯 𝛯 𝜉 𝜉 𝜩 𝜩 𝝃 𝝃
Character 𝝣 𝝽 𝞝 𝞷
Unicode name MATHEMATICAL SANS-SERIF
BOLD CAPITAL XI
MATHEMATICAL SANS-SERIF
BOLD SMALL XI
MATHEMATICAL SANS-SERIF
BOLD ITALIC CAPITAL XI
MATHEMATICAL SANS-SERIF
BOLD ITALIC SMALL XI
Encodings decimal hex decimal hex decimal hex decimal hex
Unicode 120675 U+1D763 120701 U+1D77D 120733 U+1D79D 120759 U+1D7B7
UTF-8 240 157 157 163 F0 9D 9D A3 240 157 157 189 F0 9D 9D BD 240 157 158 157 F0 9D 9E 9D 240 157 158 183 F0 9D 9E B7
UTF-16 55349 57187 D835 DF63 55349 57213 D835 DF7D 55349 57245 D835 DF9D 55349 57271 D835 DFB7
Numeric character reference 𝝣 𝝣 𝝽 𝝽 𝞝 𝞝 𝞷 𝞷

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.

References[edit]

  1. ^ "xi". New Oxford American Dictionary, 2nd Edition.
  2. ^ SPIE Optipedia article: "Spatial Frequency"
  3. ^ Unicode Code Charts: Greek and Coptic (Range: 0370-03FF)