turnout has 9 distinct synonyms spread across 4 of its 7 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.
the group that gathers together for a particular occasion
“a large turnout for the meeting”
a short stretch of railroad track used to store rolling stock or enable trains on the same line to pass
attendance for a particular event or purpose (as to vote in an election)
“the turnout for the rally”
(ballet) the outward rotation of a dancer's leg from the hip
Synonyms, antonyms and the broader and narrower relations for turnout come from Princeton University’s WordNet. Full sources and licences.