From Middle English dungeon, dungeoun, dungun (“castle keep, prison cell below the castle, dungeon”), from Old French donjon (“castle keep”), from Frankish *dungjo (“prison, dungeon, underground cellar”), from Proto-Germanic *dungijō, *dungijǭ (“enclosed space, vault, bower, treasury”), from Proto-Germanic *dungaz, *dungō (“dung, manure”), from Proto-Indo-European *dʰengʰ- (“to cover”). Cognate with Old English dung (“prison, dungeon”), Old Saxon dung (“underground cellar”), Old High German tung ("underground cellar"; > German Tunk (“manure or soil covered basement, underground weaving workshop”)), Old Norse dyngja ("a detached apartment, a lady's bower"; > Icelandic dyngja (“chamber”)). More at dung.
The game term has been popularized by Dungeons & Dragons.
- An underground prison or vault, typically built underneath a castle.
- (obsolete) The main tower of a motte or castle; a keep or donjon.
- (games) An underground area inhabited by enemies, containing story objectives, treasure and bosses.
Derived terms 
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