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 them from certain digraphs which had become homophonous, as follows: The letters of the alphabet were used in the system of Greek numerals. For this purpose the letters digamma and qoppa (but not san) were retained although they had gone out of general use, and the obscure letter sampi was added at the end of the alphabet. Digamma was often replaced in numerical use by stigma (Ϛ), originally a ligature of sigma and tau, or even the sequence sigma-tau (στ'). The Old Italic and Anatolian alphabets are, like the Greek alphabet, attested from the 8th century BC. It is unclear