A person or thing that blocks, especially in sports, someone who prevents an opponent from advancing. The offensive lineman served as an effective blocker, preventing the defensive players from reaching the quarterback.
A substance or device that prevents or restricts a particular action or process. The doctor prescribed a beta blocker to help manage the patient's high blood pressure.
A person who obstructs or hinders progress or action. The project manager identified a blocker in the workflow that was causing delays in the project timeline.