Xi (/zaɪ/ZY or /(k)saɪ/ (K)SY; uppercase Ξ, lowercase ξ; Greek: ξι) is the fourteenth letter of the Greek alphabet, representing the voiceless consonant cluster. Its name is pronounced [ksi] in both Ancient Greek and Modern Greek. In the system of Greek numerals, it has a value of 60. Xi was derived from the Phoenician letter samekh (𐤎).
Xi is distinct from the letter chi, which gave its form to the Latin letter X.
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