The earliest attestation of the word zodiac is in 1390 CE from English poet John Gower's seminal epic Confessio Amantis, where he writes about twelve signs "compassed in the zodiaque". Here, Gower just borrowed an Old French word to use in his writing, and that came from Latin zodiacus, still with the same definition. Zodiacus is a shortening of the Ancient Greek phrase zodiakos kyklos, which literally translates to "circle of little animals", something that makes a lot of sense if you think about it. The zodiakos part of that is a diminutive of zoion, the word for "animal" in general (and where the zoo- part in zoology comes from). This, through Proto-Hellenic, finally traces to the Proto-Indo-European reconstruction geyh, "to live". Usage of the word zodiac through history peaked in the 1790s and has been relatively constant throughout the twentieth and twenty-first centuries.
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.