General term for a person or device that blocks something, such as an ad blocker or a blocker in a game.
I installed an ad blocker.
In sports, a player who blocks opponents, e.g., in volleyball or American football.
He is active as a blocker in volleyball.
blocker (pharmacology); antagonist
In pharmacology, a substance that blocks a receptor or physiological process, such as a beta-blocker.
This drug acts as a calcium blocker.
You need to turn off your ad blocker to view this site.
He is playing an active role as the team's blocker.
The doctor recommended taking a beta-blocker.