Chi (

uppercase Letter case is the distinction between the letters that are in larger uppercase or capitals (or more formally ''majuscule'') and smaller lowercase (or more formally ''minuscule'') in the written representation of certain languages. The writing ...

Χ,

lowercase Letter case is the distinction between the letters that are in larger uppercase or capitals (or more formally ''majuscule'') and smaller lowercase (or more formally ''minuscule'') in the written representation of certain languages. The writing ...

χ; el, χῖ) is the 22nd letter of the

Greek alphabet The Greek alphabet has been used to write the Greek language since the late 9th or early 8th century BCE. It is derived from the earlier Phoenician alphabet, and was the earliest known alphabetic script to have distinct letters for vowels as w ...

Greek

Pronunciation

Ancient Greek

Its value in

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic p ...

was an aspirated velar stop (in the

Western Greek alphabet Many local variants of the Greek alphabet were employed in ancient Greece during the archaic and early classical periods, until around 400 BC, when they were replaced by the classical 24-letter alphabet that is the standard today. All forms ...

: /ks/).

Koine Greek

Koine Greek Koine Greek (; Koine el, ἡ κοινὴ διάλεκτος, hē koinè diálektos, the common dialect; ), also known as Hellenistic Greek, common Attic, the Alexandrian dialect, Biblical Greek or New Testament Greek, was the common supra-reg ...

and later dialects it became a

fricative A fricative is a consonant produced by forcing air through a narrow channel made by placing two articulators close together. These may be the lower lip against the upper teeth, in the case of ; the back of the tongue against the soft palate in t ...

(/) along with Θ and Φ.

Modern Greek

Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ), refers collectively to the dialects of the Greek language spoken in the modern era, including the official standardized form of the ...

, it has two distinct pronunciations: In front of high or front vowels ( or ) it is pronounced as a

voiceless palatal fricative The voiceless palatal fricative is a type of consonantal sound used in some spoken languages. The symbol in the International Phonetic Alphabet that represents this sound is , and the equivalent X-SAMPA symbol is C. It is the non-sibilant equi ...

, as in

German German(s) may refer to: * Germany (of or related to) ** Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...

''ich'' or like the ''h'' in some pronunciations of the

English English usually refers to: * English language * English people English may also refer to: Peoples, culture, and language * ''English'', an adjective for something of, from, or related to England ** English national ide ...

words ''hew'' and ''human''. In front of low or back vowels (, or ) and

consonants In articulatory phonetics, a consonant is a speech sound that is articulated with complete or partial closure of the vocal tract. Examples are and pronounced with the lips; and pronounced with the front of the tongue; and pronounced wit ...

, it is pronounced as a

voiceless velar fricative The voiceless velar fricative is a type of consonantal sound used in some spoken languages. It was part of the consonant inventory of Old English and can still be found in some dialects of English, most notably in Scottish English, e.g. in ''loc ...

(), as in German ''ach'' or

Spanish Spanish might refer to: * Items from or related to Spain: **Spaniards are a nation and ethnic group indigenous to Spain **Spanish language, spoken in Spain and many Latin American countries **Spanish cuisine Other places * Spanish, Ontario, Can ...

''j''.

Transliteration

Chi is romanized as in most systematic transliteration conventions, but sometimes is used. In addition, in Modern Greek, it is often also romanized as or in informal practice.

Greek numeral

In the system of

Greek numerals Greek numerals, also known as Ionic, Ionian, Milesian, or Alexandrian numerals, are a system of writing numbers using the letters of the Greek alphabet. In modern Greece, they are still used for ordinal numbers and in contexts similar to tho ...

, it has a value of 600.

Xi

In ancient times, some local forms of the

used the chi instead of xi to represent the /ks/ sound. This was borrowed into the early

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

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 The Latin alphabet or Roman alphabet is the collection of letters originally used by the ancient Romans to write the Latin language. Largely unaltered with the exception of extensions (such as diacritics), it used to write English and th ...

Cyrillic

Chi was also included in the

Cyrillic script The Cyrillic script ( ), Slavonic script or the Slavic script, is a writing system used for various languages across Eurasia. It is the designated national script in various Slavic, Turkic, Mongolic, Uralic, Caucasian and Iranic-speaking co ...

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 (dialogue), Timaeus'', it is explained that the two bands that form the Anima mundi (spirit), 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#.CE.A7, 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

Coptic khi

Latin chi

Mathematical chi

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

\chi^2

has Chi-squared (disambiguation), 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, Chiasm (anatomy), crossings of Peripheral nervous system, peripheral nerves (such as the optic chiasm) are named for the letter Chi because of its Χ-shape. In chemistry, the mole fraction and electronegativity may be denoted by the lowercase

\chi

. In physics,

\chi

denotes electric susceptibility, 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.

References

Greek letters Phonetic transcription symbols