เอปไซลอน

Also known as ε, epsilon

Epsilon (, uppercase ', lowercase or '; ) is the fifth letter of the Greek alphabet, corresponding phonetically to a mid front unrounded vowel or . In the system of Greek numerals it also has the value five. It was derived from the Phoenician letter He (𐤄‎). Letters that arose from epsilon include the Roman E, Ë and Ɛ, and Cyrillic Е, È, Ё, Є and Э. The name of the letter was originally ( ), but it was later changed to ( 'simple e') in the Middle Ages to distinguish the letter from the digraph , a former diphthong that had come to be pronounced , and because the digraph had become unsuitable