Cuneiform zu, (also sú, ṣú, and Sumerogram ZU (capital letter majuscule)), is an uncommon-use sign in the 1350s BC Amarna letters, the Epic of Gilgamesh, and other cuneiform texts.
In the Epic of Gilgamesh, Sumerogram ZU is used to spell the name of god Ninazu, (a name of god Tammuz, two times, Chapter XII, 28, 47).
In the Epic, ZU is also used as a logogram, ZU.AB, for Akkadian language "apsû",[1][2] English language "abyss"; it is used twice in Chapter VIII, and twice in Chapter XI, the Gilgamesh flood myth.
It was also used to name Giant Squid Studios' game, Abzû.
The usage numbers for zu in the Epic of Gilgamesh are as follows:[3] sú-(1) time, ṣú-(0), zu-(41), and ZU-(7) times.