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Origin Adapted from Phoenician consonantal script, about the 8th century BCE
Chi is the twenty-second letter of the Greek alphabet, one of the Greek additions made for the aspirated k and shaped like an X. It sounds that aspirated k in classical Greek, which became the ch of German Bach or Scottish loch in later Greek, and its value in isopsephy is six hundred, placing it six hundredth in the numeral order. In the Western Greek alphabets the X shape instead carried the ks sound, and that Western value passed into Latin as X. Chi is deeply symbolic: with Rho it forms the Chi-Rho Christogram, an early monogram of Christ, the first two letters of Christos, while alone it is the initial X used as an abbreviation for Christ, as in Xmas. Its X shape is the St Andrew's cross, the diagonal cross on which the apostle Andrew was martyred, and a general mark of crossing and of the unknown. In statistics the chi-squared test and distribution are fundamental.
Facts
Origins
Origin PeriodAdapted from Phoenician consonantal script, about the 8th century BCE 1Tradition: The Greek alphabet and the Milesian numerals Origin PeriodEvery European alphabet descends from that decision 1Tradition: The Greek alphabet and the Milesian numerals Origin PeriodInnovation: wrote vowels with letters of their own 1Tradition: The Greek alphabet and the Milesian numerals Place of OriginPrecise place disputed: Al Mina, Cyprus, Crete, Euboea all argued for 1Tradition: The Greek alphabet and the Milesian numerals Place of OriginThe Aegean world, at a point of contact with Phoenician traders 1Tradition: The Greek alphabet and the Milesian numerals Origin of the NameAlpha, beta, gamma are aleph, bet, gimel: ox, house, camel 1Tradition: The Greek alphabet and the Milesian numerals Origin of the NameClearest evidence the alphabet was taken over, not invented 1Tradition: The Greek alphabet and the Milesian numerals Origin of the NameGreek letter names are borrowed Semitic words meaning nothing in Greek 1Tradition: The Greek alphabet and the Milesian numerals Origin of the NameNo Phoenician ancestor; east and west Greek disagreed on its sound 1Tradition: The Greek alphabet and the Milesian numerals Origin of the NameOne of four supplementary letters added at the end of the Greek alphabet 1Tradition: The Greek alphabet and the Milesian numerals Origin of the NameThat disagreement survives in the Latin X 1Tradition: The Greek alphabet and the Milesian numerals Sense of the NameA Greek creation, not inherited from Phoenician; added among the supplementary letters devised for the aspirated sound Phoenician had no sign for. 1 Identity
Script TypeAn alphabet: each letter writes a single sound, consonant or vowel, inherited from Phoenician's twenty-two consonantal signs but repurposing several of them, for the first time in the alphabet's history, to write vowels outright. 1 PositionTwenty-second of twenty-four in the Greek alphabet 1 Attributions
Associated SoundAspirated k in classical Greek, become the ch of German Bach or Scottish loch in later Greek 1 Attestation
Meaning in the Attesting SourceIsopsephy (Greek gematria) attested in inscriptions and magical papyri 1Tradition: The Greek alphabet and the Milesian numerals Meaning in the Attesting SourceThe 27-sign series used three lost letters: digamma/stigma, koppa, sampi 1Tradition: The Greek alphabet and the Milesian numerals Meaning in the Attesting SourceThis atlas's 24 letters hold none of those three 1Tradition: The Greek alphabet and the Milesian numerals Learn More
Chi: The Greek Letter (Value 600)
Chi is the twenty-second Greek letter, a Greek innovation without a Phoenician model; its value is 600. Chi carries strong genuine symbolism as the first letter of Christos: it forms the Chi-Rho monogram and stands alone as an abbreviation for Christ (as in 'Xmas'). Its cross shape also gives the rhetorical term chiasmus its name.
The Greek letters doubled as numerals in the Milesian (alphabetic) system, in which each letter carried a fixed value; the practice of summing a word's letters into a number, called isopsephy, is the Greek counterpart of Hebrew gematria and appears in inscriptions, the Greek Magical Papyri and early Christian texts. Chi is one of four supplementary letters, together with Phi, Psi and Omega, added at the end of the Greek alphabet once its Phoenician-derived series had run out; unlike the borrowed letters it has no Semitic ancestor, and the disagreement between east and west Greek dialects over its sound survives today in the Latin letter X. Its isopsephy value of 600 belongs to the Milesian alphabetic numeral system, which also needed three further, otherwise obsolete letters, digamma (also called stigma), koppa and sampi, to cover every value from 1 up to 900; none of the three survives among the 24 letters in ordinary use today.
Chi in Modern Use
Chi shares in the Chi-Rho monogram discussed under rho elsewhere in this atlas, formed by overlaying chi's crossed strokes on rho's single stroke to abbreviate the Greek Christos, Christ; the same abbreviating logic survives independently in the English word Xmas, which uses the Latin letter X to stand in for chi and, by extension, for Christ, a usage documented in English at least since the 16th century and often mistaken today for a purely secular shortening rather than a centuries-old scribal abbreviation.
In modern statistics, chi-squared, written with a superscript two after the letter, denotes one of the most widely used tests in the field, developed chiefly by Karl Pearson around 1900 to measure how far observed data departs from an expected distribution, a tool now standard across the sciences and social sciences alike. Chi also appears in physics as a symbol for electric susceptibility and other technical coefficients. None of these uses, ancient or modern, draws on chi's own classical Greek sound value or its place in the Milesian numeral system, both covered elsewhere in this atlas; the letter's afterlife runs almost entirely through its graphic resemblance to a cross, X, rather than through its spoken value.
Cross-Tradition Connections
Derived from This
Why this is disputed. Glagolitic Heru was added partly to spell Greek loanwords and names, inheriting Chi's numeral value directly (600), even though the kh sound itself also occurs natively in Slavonic. What remains disputed is the letterform Cyril gave it: the mainstream palaeographic school derives its ornamental shape from medieval Greek cursive minuscule, the same source claimed for the alphabet's core letters, while the rival idiographic school holds Glagolitic's letterforms, this one included, were substantially invented rather than borrowed from any existing script.
Kher takes its shape from Greek chi and its numeral value of 600 from the same letter. Where the Slavonic NAME kher came from is a separate and unsettled question.
Taken over chiefly for loanwords and for the contracted sacred names
The Latin letter X descends from Greek Chi, reaching Latin through the Etruscan adaptation of a Western Greek alphabet. The Western Greek alphabets used chi for the cluster ks, and that is the value Latin took. The Ionic alphabet that became standard Greek used the same sign for an aspirated k.
Related To
Coptic Khi is the Greek chi, an aspirated k Coptic also uses as shorthand for kappa plus hori; both carry the numeral value 600.
X took its shape and ks value from the Western Greek alphabet's letter for the aspirated ch sound, Chi, one of two Greek candidates its own history names.
Chi lent its shape and aspirated-k value to a Western Greek alternate letter for the ks sound, and that Western value passed into Latin as X; Roman X already names Chi as one of its two Greek candidates.
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