WordNet records no synonym and no antonym for pelagius. 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 British or Irish monk who denied the doctrines of original sin and predestination and defended human goodness and free will; his views were declared heretical by the Council of Ephesus in 431 (circa 360-418)
Synonyms, antonyms and the broader and narrower relations for pelagius come from Princeton University’s WordNet. Full sources and licences.