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.