circumstance has 4 distinct synonyms spread across 2 of its 4 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 condition that accompanies or influences some event or activity
the set of facts or circumstances that surround a situation or event
“the historical context”
Synonyms, antonyms and the broader and narrower relations for circumstance come from Princeton University’s WordNet. Full sources and licences.
information that should be kept in mind when making a decision
“another consideration is the time it would take”
formal ceremony about important occasions
“pomp and circumstance”