Zeta
From Textus Receptus
Zeta (uppercase Ζ, lowercase ζ; Greek: Ζήτα [ziːta] Zita) is the sixth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 7. It was derived from the Phoenician letter Zayin . Letters that arose from Zeta include the Roman Z and Cyrillic З (Ze).
Unlike the other Greek letters, this letter did not take its name from the Phoenician letter it was derived from; it was given a new name on the pattern of beta, eta and theta.
Zeta has the numerical value 7 rather than 6 because the letter digamma (also called 'stigma' as a Greek numeral) was originally in the sixth position in the alphabet.
Zeta can be said to be the origin of the most common pronunciation of the Roman letter Z.