nicaea has 2 distinct synonyms spread across 2 of its 3 senses. 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.
an ancient city in Bithynia; founded in the 4th century BC and flourished under the Romans; the Nicene Creed was adopted there in 325
the seventh ecumenical council in 787 which refuted iconoclasm and regulated the veneration of holy images
Synonyms, antonyms and the broader and narrower relations for nicaea come from Princeton University’s WordNet. Full sources and licences.
the first ecumenical council in 325 which produced the wording of the Nicene Creed and condemned the heresy of Arianism