WordNet records no synonym and no antonym for areopagus. 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 hill to the to the west of the Athenian acropolis where met the highest governmental council of ancient Athens and later a judicial court
the highest governmental assembly in ancient Athens (later a judicial court)
Synonyms, antonyms and the broader and narrower relations for areopagus come from Princeton University’s WordNet. Full sources and licences.