stop·per (st?p??r)n.1. A device, such as a cork or plug, that is inserted to close an opening.2. One that causes something to stop: a conversation stopper.3. Games A card or cards enabling one to prevent one’s opponents from winning all the tricks in a particular suit in a hand of bridge.4. Baseball A relief pitcher, especially one called upon to protect a lead.5. Sports a. A player who excels on defense, as in basketball.b. In soccer, a defensive player who plays behind the center midfielder and often guards the opponent’s best forward. Also called center back.c. A goalie.tr.v. stop·pered, stop·per·ing, stop·pers To close with or as if with a stopper.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.