Chi (letter)#Symbolism

File:NAMA Alphabet grec.jpg vessel, with a cross-shaped chi]]

Its value in Ancient Greek was an aspirated velar stop {{IPA|/kʰ/}} (in the Western Greek alphabet: /ks/).

In Koine Greek and later dialects it became a fricative ({{IPA|[x]}}/{{IPA|[ç]}}) along with Θ and Φ.

In Modern Greek, it has two distinct pronunciations: In front of high or front vowels ({{IPA|/e/}} or {{IPA|/i/}}) it is pronounced as a voiceless palatal fricative {{IPA|[ç]}}, as in German ich or like some pronunciations of "h" in English words like hew and human. In front of low or back vowels ({{IPA|/a/}}, {{IPA|/o/}} or {{IPA|/u/}}) and consonants, it is pronounced as a voiceless velar fricative ({{IPA|[x]}}), as in German ach or Spanish j. This distinction corresponds to the ich-Laut and ach-Laut of German.

Chi is romanized as {{angle bracket|ch}} in most systematic transliteration conventions, but sometimes {{angle bracket|kh}} is used.{{Cite web |date=2024-12-20 |title=Greek language {{!}} Definition, Alphabet, Origin, & Facts {{!}} Britannica |url=https://www.britannica.com/topic/Greek-language |access-date=2025-02-09 |website=www.britannica.com |language=en |quote=Some differences in transliteration result from changes in pronunciation of the Greek language; others reflect convention, as for example the χ (chi or khi), which was transliterated by the Romans as ch (because they lacked the letter k in their usual alphabet). In Modern Greek, however, the standard transliteration for χ is kh.}} In addition, in Modern Greek, it is often also romanized as {{angle bracket|h}} or {{angle bracket|x}} in informal practice.

In the system of Greek numerals, it has a value of 600.

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.

Chi was also included in the Cyrillic script as the letter Х, with the phonetic value /x/ or /h/.

In the International Phonetic Alphabet, {{angbr IPA|ꭓ}} represents a voiceless uvular fricative.

Chi is the basis for the name literary chiastic structure and the name of chiasmus.

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 typeface with the Greek letter rho, it is called the Chi Rho and used to represent the person of Jesus Christ.

• In statistics, the term chi-squared or $\backslash chi^2$ has various uses, including the chi-squared distribution, the chi-squared test, and chi-squared target model
• In algebraic topology, Chi is used to represent the Euler characteristic of a surface.{{Cite web |last=Weisstein |first=Eric W. |title=Euler Characteristic |url=https://mathworld.wolfram.com/EulerCharacteristic.html |access-date=2025-02-09 |website=mathworld.wolfram.com |language=en}}
• The chromatic number of a graph in graph theory{{Cite web |last=Weisstein |first=Eric W. |title=Chromatic Number |url=https://mathworld.wolfram.com/ChromaticNumber.html |access-date=2025-02-09 |website=mathworld.wolfram.com |language=en |quote=The chromatic number of a graph G is most commonly denoted χ (G) (e.g., Skiena 1990, West 2000, Godsil and Royle 2001, Pemmaraju and Skiena 2003),...}}
• In neuroanatomy, crossings of peripheral nerves (such as the optic chiasm) are named for the letter Chi because of its Χ-shape.{{cite book |title=The Human Brain |last=Asimov |first=Isaac |author-link= Isaac Asimov |year=1963 |publisher=Houghton Mifflin |location=Boston}}
• In chemistry, the mole fraction{{cite book|last=Zumdahl|first=Steven S.|title=Chemistry|url=https://archive.org/details/chemistrythediti00zumd|url-access=limited|year=2008|publisher=Cengage Learning|isbn=978-0547125329|edition=8th|page=[https://archive.org/details/chemistrythediti00zumd/page/n229 201]}}{{cite book|first1=James N.|last1=Spencer|first2=George M.|last2=Bodner|first3=Lyman H.|last3=Rickard|title=Chemistry: structure and dynamics|url=https://archive.org/details/chemistrystructu00spen_759|url-access=limited|year=2010|publisher=Wiley|location=Hoboken, NJ|isbn=9780470587119|edition=5th|page=[https://archive.org/details/chemistrystructu00spen_759/page/n378 357]}} and electronegativity{{GoldBookRef|file=E01990|title=Electronegativity}} may be denoted by the lowercase $\backslash chi$.
• In physics, $\backslash chi$ denotes electric or magnetic susceptibility.{{Cite journal |last=Mugiraneza |first=Sam |last2=Hallas |first2=Alannah M. |date=2022-04-19 |title=Tutorial: a beginner’s guide to interpreting magnetic susceptibility data with the Curie-Weiss law |url=https://www.nature.com/articles/s42005-022-00853-y |journal=Communications Physics |language=en |volume=5 |issue=1 |pages=1–12 |doi=10.1038/s42005-022-00853-y |issn=2399-3650 |quote=However, for newly synthesized materials, there is one indispensable characterization technique that is as old as the field of magnetism itself: magnetic susceptibility, χ,...|arxiv=2205.07107 }}{{Cite book |last=Jiles |first=David |title=Introduction to magnetism and magnetic materials |date=2016 |publisher=CRC Press, Taylor & Francis Group |isbn=978-1-138-44149-1 |edition=Third |location=Boca Raton London New York |pages=42 |quote=We can now make a general statement for the permeability μ and susceptibility {{mvar|χ}}}}
• 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 analytic number theory, chi is used for the Dirichlet character.

• {{unichar|03A7|html=}}Unicode Code Charts: [https://www.unicode.org/charts/PDF/U0370.pdf Greek and Coptic (Range: 0370-03FF)]
• {{unichar|03C7|html=}}
• {{unichar|1D61|html=}}
• {{unichar|1D6A|html=}}
• {{unichar|2627|html=}}
• {{unichar|2CAC|html=}}
• {{unichar|2CAD|html=}}
• {{unichar|2CE9|html=}}
• {{unichar|A7B3|html=}}
• {{unichar|AB53|html=}}
• {{unichar|AB54|html=}}
• {{unichar|AB55|html=}}
• {{unichar|1D6BE|html=}}
• {{unichar|1D6D8|html=}}
• {{unichar|1D6F8|html=}}
• {{unichar|1D712|html=}}
• {{unichar|1D732|html=}}
• {{unichar|1D74C|html=}}
• {{unichar|1D76C|html=}}
• {{unichar|1D786|html=}}
• {{unichar|1D7A6|html=}}
• {{unichar|1D7C0|html=}}

{{Wiktionary|Χ|χ}}

• Chi (disambiguation)
• Х, х - Kha (Cyrillic)

Category:Greek letters

Category:Phonetic transcription symbols