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 Often, in medieval manuscripts, old uncial letter forms were mixed in with the normal minuscule letters for writing titles or for emphasizing the initial letter of a word or sentence. Like in Latin, this became the root of the modern innovation of letter case, the systematic distinction between uppercase and lowercase letters in orthography. The uppercase letters of modern orthography are derived from the uncial script, while the lowercase letters are derived from minuscules. The invention of printing saw the codification of a more fixed set of letter structures. Greek handwriting made extensive use of ligatures with letters written differently