Psi (letter) Psi (letter) Psi (; uppercase ', lowercase '; "psi" ) is the 23rd letter of the Greek alphabet and has a numeric value of 700. In both Classical and Modern Greek, the letter indicates the combination /ps/ (as in English word "lapse"). For Greek loanwords in Latin and modern languages with Latin alphabets, psi is usually transliterated as "ps". The letter's origin is uncertain. It may or may not derive from the Phoenician alphabet. It appears in the 7th century BC, expressing /ps/ in the Eastern alphabets, but /kʰ/ in the Western alphabets (the sound expressed by Χ in the
Greek alphabet of these letters is a matter of some debate. Three of the original Phoenician letters dropped out of use before the alphabet took its classical shape: the letter Ϻ ("san"), which had been in competition with Σ ("sigma") denoting the same phoneme /s/; the letter Ϙ ("qoppa"), which was redundant with Κ ("kappa") for /k/, and Ϝ ("digamma"), whose sound value /w/ dropped out of the spoken language before or during the classical period. Greek was originally written predominantly from right to left, just like Phoenician, but scribes could freely alternate between directions. For a time, a writing style with