first council of constantinople has 1 distinct synonym spread across 1 of its 1 sense. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
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 second ecumenical council in 381 which added wording about the Holy Spirit to the Nicene Creed
Synonyms, antonyms and the broader and narrower relations for first council of constantinople come from Princeton University’s WordNet. Full sources and licences.