Xi (letter)

Xi is the fourteenth letter of the Greek alphabet (uppercase Ξ, lowercase ξ; Greek: ξι), representing the voiceless consonant cluster [ks]. Its name is pronounced [ksi] in Modern Greek, and generally /z/ or /ks/ 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

A joined variant of Ξ (New Athena Unicode font)

Both in classical Ancient Greek and in Modern Greek, the letter Ξ represents the consonant cluster /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 cluster /ks/ was represented by Χ (which in classical Greek is chi, used for /kʰ/).

Because this variant of the Greek alphabet was used in Magna Graecia (the Greek colonies in Sicily and the southern part of the Italian peninsula), the Latin alphabet borrowed Χ rather than Ξ as the Latin letter that represented the /ks/ cluster that was also present in Latin.

Cyrillic

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 a symbol in various contexts.

Pure mathematics

Physics

Other uses

Lowercase

The lowercase letter ξ is used as a symbol for:

Pure mathematics

Physics and astronomy

Other uses

Character encodings

Greek Xi / Coptic Ksi

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

Character information
PreviewΞξ
Unicode name GREEK CAPITAL LETTER XI GREEK LOWERCASE LETTER XI COPTIC CAPITAL LETTER KSI COPTIC LOWERCASE LETTER KSI
Encodingsdecimalhexdechexdechexdechex
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

Mathematical Xi

The following 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.

Character information
Preview𝚵𝛏𝛯𝜉𝜩𝝃
Unicode name MATHEMATICAL 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
Encodingsdecimalhexdechexdechexdechexdechexdechex
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
Character information
Preview𝝣𝝽𝞝𝞷
Unicode name MATHEMATICAL 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
Encodingsdecimalhexdechexdechexdechex
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

Other uses

Ξ for E in a commercial logo

Uppercase Ξ is used as an 'E' to stylise company names/logos like Razer (styled as RΛZΞR), Tesla (styled as TΞSLA), musician Banners (styled as BANNΞRS), and in South Korean boy group ZE:A's newest logo (styled as "ZΞA") (Compare: Heavy Metal umlaut; Faux Cyrillic)

References

  1. "xi". New Oxford American Dictionary, 2nd Edition.
  2. SPIE Optipedia article: "Spatial Frequency"
  3. IUPAC Gold Book Entry: "Extent of Reaction" Archived June 29, 2012, at the Wayback Machine
  4. Buckingham, John; Cooper, Caroline M.; Purchase, Rupert (18 November 2015). Natural Products Desk Reference. CRC Press. pp. 53–. ISBN 978-1-4398-7362-5.
  5. Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names. 2014. pp. 1159–1160. ISBN 9780854041824. Retrieved 11 September 2017.
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