show-stopper has 2 distinct synonyms spread across 2 of its 2 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 act so striking or impressive that the show must be delayed until the audience quiets down
something that is strikingly attractive or has great popular appeal
“she has a show-stopper of a smile”
Synonyms, antonyms and the broader and narrower relations for show-stopper come from Princeton University’s WordNet. Full sources and licences.