excluder

/ɪkˈskluːdər/
noun
  1. A person or thing that prevents someone or something from entering or being included.
    • The new security guard acted as an excluder, keeping unauthorized visitors out of the building.
    • In the game, the goalie is the main excluder of the opposing team's shots.
    • This filter is an effective excluder of dust and pollen from the air.
Synonyms