A person who is imprisoned in a dungeon, or historically, a jailer or keeper of a dungeon.
From 'dungeon' (from Old French donjon, the keep of a castle, from a Germanic root) + '-er' (agent noun suffix). Can refer to either the imprisoned or the imprisoner depending on context.
Medieval dungeoners—the jailers—had one of history's creepiest jobs, essentially living in dark torture chambers; the word's ambiguity about whether it means prisoner or jailer mirrors how prisoners and jailors were often equally trapped by the system.
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