coincidence has 4 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 event that might have been arranged although it was really accidental
the quality of occupying the same position or area in space
“he waited for the coincidence of the target and the cross hairs”
Synonyms, antonyms and the broader and narrower relations for coincidence come from Princeton University’s WordNet. Full sources and licences.
the temporal property of two things happening at the same time
“the interval determining the coincidence gate is adjustable”