the.com/zeta

means The sixth letter of the Greek alphabet, written Ζ/ζ, now better known as the stand-in symbol math and science reach for in zeta functions, zeta potential, and particle names.

from From Greek zēta, inherited from the Phoenician letter zayin, itself possibly meaning 'weapon' — picture a small axe or sickle shape that got smoothed into a letterform. The Greeks passed it to the Etruscans and Romans, where it eventually gave English its 'Z' (though Latin briefly dropped it, only borrowing it back later for Greek loanwords). Its current fame as a mathematical symbol — most notably in Riemann's zeta function — comes from the old habit of raiding the Greek alphabet whenever Latin letters ran out.