This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. A dark, often underground chamber or cell used to confine prisoners.

n. A donjon.

n. An underground prison or vault, typically built underneath a castle.

n. The main tower of a motte or castle; a keep or donjon.

n. An underground area inhabited by enemies, containing story objectives, treasure and bosses.

n. A close, dark prison, commonly, under ground, as if the lower apartments of the donjon or keep of a castle, these being used as prisons.

v. To shut up in a dungeon.

n. The principal tower of a medieval castle.

n. Hence A close cell; a deep, dark place of confinement.

To confine in or as in a dungeon.

n. the main tower within the walls of a medieval castle or fortress

n. a dark cell (usually underground) where prisoners can be confined

"The occasional five-man dungeon is about the most I can manage."

oubliette   

instance dungeon    dungeon crawler   

donjon    keep   

cavern    cellar    prison    vault    basement    fortress    alley    courtyard    tomb    pit