Epsilon

Epsilon is the fifth letter of the Greek alphabet, corresponding phonetically to a mid front unrounded vowel IPA: [e̞] or IPA: [ɛ̝]. 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 εἶ, but it was later changed to ἒ ψιλόν in the Middle Ages to distinguish the letter from the digraph ⟨αι⟩, a former diphthong that had come to be pronounced, and because the digraph ⟨ει⟩ had become unsuitable due to its own shift to. In Modern Greek, its name has fused into έψιλον. Read more on Wikipedia