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 Greek. Since the names of the letters "’āleph" and "hē" were pronounced and by the Greeks, with initial vowels due to the silent gutturals (the disambiguation "e psilon" "narrow e" came later), the acrophonic principle was retained for vowels as well as consonants by using them for the Greek vowel sounds and . Only the letter "‘ayin" for necessitated a change of name ("o", later "o micron"). Phoenician also had an "emphatic" consonant, "ṭēth", which did not exist in Greek. However, Greek had an aspiration distinction that Phoenician lacked, and used ṭēth for the aspirated . The Phoenician consonants "kaph"