Chi (letter) for the design of steel structures. In graph theory, a lowercase chi is used to represent a graph's chromatic number. Chi (letter) Chi (uppercase Χ, lowercase χ; ) is the 22nd letter of the Greek alphabet, pronounced or in English. Its value in Ancient Greek was an aspirated velar stop (in the Western Greek alphabet: /ks/). In Koine Greek and later dialects it became a fricative (/) along with Θ and Φ. In Modern Greek, it has two distinct pronunciations: In front of high or front vowels ( or ) it is pronounced as a voiceless palatal fricative , as
History of the Greek alphabet Phoenician values, but with different forms: as the Greek letter digamma for the consonant , and as the letter upsilon for the vowel . Upsilon was added at the end of the alphabet, perhaps to avoid upsetting the alphabetic order that was used in Greek numerals. Phoenician "hē" had been used as a "mater lectionis" for both and in addition to , but in Greek it was restricted to , following the acrophonic principle; its value was instead written with the letter "’āleph", while Greek was written with "ḥeth". All Phoenician letters had been acrophonic, and they remained so in