WordNet records no synonym and no antonym for classical mythology. It is the only member of its synset, 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.
the system of mythology of the Greeks and Romans together; much of Roman mythology (especially the gods) was borrowed from the Greeks
Synonyms, antonyms and the broader and narrower relations for classical mythology come from Princeton University’s WordNet. Full sources and licences.