Xi (letter)

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

Xi is distinct from the letter chi, which gave its form to the Latin letter X.

Greek

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

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

Mathematics and science

Uppercase

The uppercase letter Ξ is used as symbol for:

Lowercase

The lowercase letter ξ is used as a symbol for:

Character encodings

  • Greek Xi / Coptic Ksi
CharacterΞξ
Unicode nameGREEK CAPITAL LETTER XIGREEK LOWERCASE LETTER XICOPTIC CAPITAL LETTER KSICOPTIC LOWERCASE LETTER KSI
Encodingsdecimalhexdecimalhexdecimalhexdecimalhex
Unicode926U+039E958U+03BE11420U+2C9C11421U+2C9D
UTF-8206 158CE 9E206 190CE BE226 178 156E2 B2 9C226 178 157E2 B2 9D
Numeric character referenceΞΞξξⲜⲜⲝⲝ
Named character referenceΞξ
DOS Greek1418D165A5
DOS Greek-2189BD232E8
Windows 1253206CE238EE
TeX\Xi\xi

[6]

  • Mathematical Xi
Character𝚵𝛏𝛯𝜉𝜩𝝃
Unicode nameMATHEMATICAL BOLD
CAPITAL XI
MATHEMATICAL BOLD
LOWERCASE XI
MATHEMATICAL ITALIC
CAPITAL XI
MATHEMATICAL ITALIC
LOWERCASE XI
MATHEMATICAL BOLD ITALIC
CAPITAL XI
MATHEMATICAL BOLD ITALIC
LOWERCASE XI
Encodingsdecimalhexdecimalhexdecimalhexdecimalhexdecimalhexdecimalhex
Unicode120501U+1D6B5120527U+1D6CF120559U+1D6EF120585U+1D709120617U+1D729120643U+1D743
UTF-8240 157 154 181F0 9D 9A B5240 157 155 143F0 9D 9B 8F240 157 155 175F0 9D 9B AF240 157 156 137F0 9D 9C 89240 157 156 169F0 9D 9C A9240 157 157 131F0 9D 9D 83
UTF-1655349 57013D835 DEB555349 57039D835 DECF55349 57071D835 DEEF55349 57097D835 DF0955349 57129D835 DF2955349 57155D835 DF43
Numeric character reference𝚵𝚵𝛏𝛏𝛯𝛯𝜉𝜉𝜩𝜩𝝃𝝃
Character𝝣𝝽𝞝𝞷
Unicode nameMATHEMATICAL SANS-SERIF
BOLD CAPITAL XI
MATHEMATICAL SANS-SERIF
BOLD LOWERCASE XI
MATHEMATICAL SANS-SERIF
BOLD ITALIC CAPITAL XI
MATHEMATICAL SANS-SERIF
BOLD ITALIC LOWERCASE XI
Encodingsdecimalhexdecimalhexdecimalhexdecimalhex
Unicode120675U+1D763120701U+1D77D120733U+1D79D120759U+1D7B7
UTF-8240 157 157 163F0 9D 9D A3240 157 157 189F0 9D 9D BD240 157 158 157F0 9D 9E 9D240 157 158 183F0 9D 9E B7
UTF-1655349 57187D835 DF6355349 57213D835 DF7D55349 57245D835 DF9D55349 57271D835 DFB7
Numeric character reference𝝣𝝣𝝽𝝽𝞝𝞝𝞷𝞷

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.

Other uses

Uppercase Ξ is used as an 'E' to stylise company names/logos like Razer (styled as RΛZΞR) and musician Banners (styled as BANNΞRS). (Compare: Heavy Metal umlaut; Faux Cyrillic)

References

  1. "xi". New Oxford American Dictionary, 2nd Edition.
  2. IUPAC Gold Book Entry: "Extent of Reaction" Archived June 29, 2012, at the Wayback Machine
  3. John Buckingham; Caroline M. Cooper; Rupert Purchase (18 November 2015). Natural Products Desk Reference. CRC Press. pp. 53–. ISBN 978-1-4398-7362-5.
  4. Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names. p. 1159–1160. Retrieved 11 September 2017.
  5. SPIE Optipedia article: "Spatial Frequency"
  6. Unicode Code Charts: Greek and Coptic (Range: 0370-03FF)
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