gregory has 15 distinct synonyms spread across 6 of its 6 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.
(Roman Catholic Church) a church father known for his constant fight against perceived heresies; a saint and Doctor of the Church (329-391)
Italian pope from 1831 to 1846; conservative in politics and theology; worked to propagate Catholicism in England and the United States (1765-1846)
the pope who sponsored the introduction of the modern calendar (1572-1585)
the Italian pope from 1406 to 1415 who worked to end the Great Schism and who retired to make it possible (1327-1417)
the Italian pope who fought to establish the supremacy of the pope over the Roman Catholic Church and the supremacy of the church over the state (1020-1085)
(Roman Catholic Church) an Italian pope distinguished for his spiritual and temporal leadership; a saint and Doctor of the Church (540?-604)
Synonyms, antonyms and the broader and narrower relations for gregory come from Princeton University’s WordNet. Full sources and licences.