Merriam-Webster Collegiate Dictionary - stopper

 I. noun  Date: 15th century  1. one that brings to a halt or causes to stop operating or functioning ; check: as  a. a playing card that will stop the running of a suit  b. a baseball pitcher depended on to win important games or to stop a losing streak; also an effective relief pitcher  2. one that closes, shuts, or fills up; specifically something (as a bung or cork) used to plug an opening  II. transitive verb  (~ed; ~ing)  Date: circa 1769 to close or secure with or as if with a ~ ~ the bottle