A person who arrests someone, or a device that stops or slows something down.
From arrest plus -er suffix meaning 'one who does the action.' As a device, it follows technical naming conventions (like 'starter' in an engine). The word works for both human agents and mechanical ones.
Lightning arresters are fascinating devices on buildings and power lines that safely channel electricity to the ground, preventing fires—basically giving electricity a safe 'arrest' path to follow.
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