definition of epsilon
Epsilon (uppercase Îµ, lowercase Îµ or lunate Ïµ; Greek: Î­ÏÎ¹Î»Î¿Î½) is the fifth letter of the Greek alphabet, corresponding phonetically to a mid front unrounded vowel /e/. In the system of Greek numerals it has the value five. It was derived from the Phoenician letter He .