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
Greek alphabet late ninth century BC or early eighth century BC, the Greek alphabet emerged. The period between the use of the two writing systems, during which no Greek texts are attested, is known as the Greek Dark Ages. The Greeks adopted the alphabet from the earlier Phoenician alphabet, one of the closely related scripts used for the West Semitic languages. However, the Phoenician alphabet is limited to consonants. When it was adopted for writing Greek, certain consonants were adapted to express vowels. The use of both vowels and consonants makes Greek the first alphabet in the narrow sense, as distinguished from