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
Latin alphabet Hyginus in "Fab. 277" mentions the legend that it was Carmenta, the Cimmerian Sibyl, who altered fifteen letters of the Greek alphabet to become the Latin alphabet, which her son Evander introduced into Latium, supposedly 60 years before the Trojan War, but there is no historically sound basis to this tale.) The Ancient Greek alphabet was in turn based upon the Phoenician abjad. From the Cumae alphabet, the Etruscan alphabet was derived and the Romans eventually adopted 21 of the original 27 Etruscan letters: Latin included 21 different characters. The letter was the western form of the Greek gamma, but