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
History of the Greek alphabet becoming the first 'true' alphabet. Apparently, some thirty years later, the same alphabet was introduced to Boeotia, having been adopted perhaps a little earlier in Macedonia, and went on in the course of the 4th century to displace the local alphabets throughout the whole Greek-speaking world. The Ionic alphabet included a new letter, omega, at the end of the alphabet, and standardised the representation of various sounds that had varied from one dialect to another, as follows: The absence of a letter for was of no consequence for the Ionic dialects, but sometimes led to ambiguities in Attic, which had