WordNet records no synonym and no antonym for pelagianism. 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 theological doctrine put forward by Pelagius which denied original sin and affirmed the ability of humans to be righteous; condemned as heresy by the Council of Ephesus in 431
Synonyms, antonyms and the broader and narrower relations for pelagianism come from Princeton University’s WordNet. Full sources and licences.