zodiacyoudaoicibaDictYouDict[zodiac 词源字典]
zodiac: [14] The zodiac is etymologically a circle of ‘little animals’. Greek zóidion originally denoted a ‘carved figure of an animal’ (it was a diminutive of zóion ‘animal’, a relative of English zoo). From it was derived the adjective zōidiakós, which was used in the expression zōidiakós kúklos ‘circle of carved figures’, denoting the twelve figures or signs representing the divisions of a band around the celestial sphere. Zōidiakós became a noun in its own right, and passed into English via Latin zōdiacus and French zodiaque.
=> zoo[zodiac etymology, zodiac origin, 英语词源]
zodiac (n.)youdaoicibaDictYouDict
late 14c., from Old French zodiaque, from Latin zodiacus "zodiac," from Greek zodiakos (kyklos) "zodiac (circle)," literally "circle of little animals," from zodiaion, diminutive of zoion "animal" (see zoo).

Libra is not an animal, but it was not a zodiac constellation to the Greeks, who reckoned 11 but counted Scorpio and its claws (including what is now Libra) as a "double constellation." Libra was figured back in by the Romans. In Old English the zodiac was twelf tacna "the twelve signs," and in Middle English also Our Ladye's Waye and the Girdle of the Sky.