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 for Semitic languages, and these "matres lectionis", as well as several Phoenician letters which represented consonants not present in Greek, were adapted according to the acrophonic principle to represent Greek vowels consistently, if not unambiguously. The Greek alphabet was developed by a Greek with first-hand experience of contemporary Phoenician script. Almost as quickly as it was established in the Greek mainland, it was rapidly re-exported, eastwards to Phrygia, where a similar script was devised. It was also exported westwards with Euboean or West Greek traders, where the Etruscans adapted the Greek alphabet to their own language, which eventually led to