Merriam-Webster's Collegiate® Dictionary, 11th Edition
STOPPER
I. noun
Date: 15th century
one that brings to a halt or causes to stop operating or functioning ; check : as, a playing card that will stop the running of a suit, a baseball pitcher depended on to win important games or to stop a losing streak, one that closes, shuts, or fills up,
II. transitive verb (stoppered; stoppering)
Date: circa 1769
to close or secure with or as if with a stopper