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 alphabet Greeks. From the Etruscans, a tribe living in the first millennium BCE in central Italy, and the Western Greeks, the Latins adopted writing in about the seventh century. In adopting writing from these two groups, the Latins dropped four characters from the Western Greek alphabet. They also adapted the Etruscan letter F, pronounced 'w,' giving it the 'f' sound, and the Etruscan S, which had three zigzag lines, was curved to make the modern S. To represent the G sound in Greek and the K sound in Etruscan, the Gamma was used. These changes produced the modern alphabet without the