WordNet records no synonym and no antonym for neoplatonism. 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.
a system of philosophical and theological doctrines composed of elements of Platonism and Aristotelianism and oriental mysticism; its most distinctive doctrine holds that the first principle and source of reality transcends being and thought and is naturally unknowable
“Neoplatonism was predominant in pagan Europe until the 6th century”
Synonyms, antonyms and the broader and narrower relations for neoplatonism come from Princeton University’s WordNet. Full sources and licences.