𐰔

Clauson suggest that it might ultimately be derived from Ancient Greek Ζ (Z, “zeta”) through intermediaries.

𐰔 (z)

1. A letter of the Old Turkic runic script, representing /z/, used in both vowel types.

• Clauson, Gerard (1972) “z”, in The Origin of Turkic Runic Alphabet, London, pages 70 and 75
• Clauson, Gerard (1962) Turkish and Mongolian studies‎, London: Royal Asiatic Society, page 80
• Ghirshman, Roman (1948) Les Chionites-Hephtalites‎, Iran: Institut francais d'archeologie orientale, page 63