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 and "qōph" represented sounds that were not distinctive in Greek—at most, they may have been identified with allophones determined by the following vowel. The letter qoppa was used in certain Greek dialects (notably the western dialects, which ultimately gave rise to Etruscan and eventually the Latin alphabet), but elsewhere dropped out of general use. It is possible that qoppa had been assigned to the Ancient Greek , and when that sound shifted to , the letter qoppa continued as the letter phi. Phoenician had three letters, "sāmekh, ṣādē" and "šin", representing three or probably four voiceless sibilant sounds, whereas Greek