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
Letter (alphabet) and order of appearance correspond closely. The Greek alphabet, adapted around 800 BCE, added four letters. This was the first alphabet assigning letters not only to consonant sounds, but also to vowels. The Roman Empire brought the development and refinement of our Roman alphabet, beginning around 500 BCE. The Romans added or dropped certain letters to accommodate Greek and Etruscan words; they also experimented with styles such as cursive when writing in ink. By about the fifth century CE, the beginnings of lowercase letterforms began to emerge in Roman writing, but they did not come into common use until the