congregation has 3 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.
a group of people who adhere to a common faith and habitually attend a given church
an assemblage of people or animals or things collected together
“a congregation of children pleaded for his autograph”
Synonyms, antonyms and the broader and narrower relations for congregation come from Princeton University’s WordNet. Full sources and licences.