stopper

Concise Oxford English Dictionary © 2008 Oxford University Press:
stopper/ˈstɒpə(r)/

▶noun

• 1 a plug for sealing a hole, especially in the neck of a bottle.

• 2 (in soccer or American football) a player whose function is to block attacks on goal from the middle of the field.

  ■ Baseball a pitcher who prevents opponents from scoring highly.

• 3 (in sailing or climbing) a rope or clamp for preventing a rope or cable from being run out.

▶verb (usu. as adj. stoppered) seal with a stopper.

– phrases
put a (or the) stopper on informal prevent.