dungeon

From Middle English dongeoun (“keep of a castle; dungeon; abyss, cave, den; whirlpool”), from Anglo-Norman donjun (“keep of a castle; keep used as a prison; dungeon”) and continental Old French donjon (“keep of a castle”), from Vulgar Latin *dominiōnem, seemingly derived from Latin dominus (“master, lord”) perhaps via some figurative sense like “dominant building”. Doublet of donjon. The sense of “prison (associated with a castle)”, first attested in Anglo-Norman (13th c.) and apparently never in continental Old French, likely developed in combination with Old English dung (“underground prison cell”), whence Middle English donge (“pit, abyss”, senses that are also attested for Middle English dongeoun).

The game term has been popularized by Dungeons & Dragons.