WordNet records no synonym and no antonym for zodiac. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a belt-shaped region in the heavens on either side to the ecliptic; divided into 12 constellations or signs for astrological purposes
(astrology) a circular diagram representing the 12 zodiacal constellations and showing their signs
Synonyms, antonyms and the broader and narrower relations for zodiac come from Princeton University’s WordNet. Full sources and licences.