stopper

(noun) an act so striking or impressive that the show must be delayed until the audience quiets down. Synonyms: show-stopper, showstopper.

(noun) a remark to which there is no polite conversational reply. Synonyms: conversation stopper.

(noun) (bridge) a playing card with a value sufficiently high to insure taking a trick in a particular suit. Example: "If my partner has a spade stopper i can bid no trump."

(noun) blockage consisting of an object designed to fill a hole tightly. Synonyms: plug, stopple.

(verb) close or secure with or as if with a stopper. Synonyms: stopple. Examples: "She stoppered the wine bottle." "The mothers stoppered their babies' mouths with pacifiers."