Synonyms for Stopper (same or very similar meaning)
WordNet sense 1 (an act so striking or impressive that the show must be delayed until the audience quiets down):
showstopper, show-stopper
WordNet sense 2 (a remark to which there is no polite conversational reply):
conversation stopper
WordNet sense 3 (blockage consisting of an object designed to fill a hole tightly):
plug, stopple
From the ODE community, based on WordNet
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