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 (letter). In the 8th to 6th centuries, local or "epichoric" variants of the alphabet developed. They are classified into three main groups, following Adolf Kirchhoff (1887): green (Cretan), red (Euboean or Western) and blue (Ionic, Attic and Corinthian). The main distinction is in the supplemental signs added to the Phoenician core inventory. With the exception of the early Fayum alphabet, which does not fit into the tripartite scheme, all abecedaries add Υ to the Phoenician inventory. The green alphabets have only this; the red add Φ for , Χ for , and Ψ for ; and the blue add Φ