Xi (letter)
Xi (uppercase Ξ, lowercase ξ) is the 14th letter of the Greek alphabet. It is pronounced in Modern Greek, and generally /zaɪ/ or /saɪ/ in English. In the system of Greek numerals, it has a value of 60. Xi was derived from the Phoenician letter samekh .
Xi is not to be confused with the letter chi, which gave its form to the Latin letter X.