One who bars or blocks; a person or thing that creates a barrier or obstruction.
From bar (Old French barre, meaning to block or obstruct) + -er (agent suffix meaning one who does). The term can be literal (one who bars a door) or metaphorical (one who obstructs progress).
In legal history, a 'barrer' was specifically someone who challenged or opposed a legal claim—they literally 'barred' your path to victory in court through procedural objections.
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