WordNet records no synonym and no antonym for monophysitism. 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 Christian heresy of the 5th and 6th centuries that challenged the orthodox definition of the two natures (human and divine) in Jesus and instead believed there was a single divine nature
Synonyms, antonyms and the broader and narrower relations for monophysitism come from Princeton University’s WordNet. Full sources and licences.