early 14c., "member of a militant 1st century Jewish sect which fiercely resisted the Romans in Palestine," from Late Latin zelotes, from Greek zēlōtēs "one who is a zealous follower," from zēloōn "to be zealous," from zēlos "zeal" (see zeal). Extended sense of "a fanatical enthusiast" first recorded 1630s (earlier in this sense was zelator, mid-15c.).

c. 1400, from Middle French zede, from Late Latin zeta, from Greek zēta, from Hebrew zayin, letter name, literally "weapon;" so called in reference to the shape of this letter in ancient Hebrew. U.S. pronunciation zee is first attested 1670s. Other dialectal names for the letter are izzard, ezod, uzzard, and zod.