Dungeon

(dŭn'jun), n. [Fr. dongeon, or donjon, tower or platform in the midst of a castle, turret, or closet on the top of a house, a castle-keep, Pr. donjon, donjô, domejô, L. Lat. dunjo, dongio, dangio, domgio, domnio, either from Ir. daingean, strong-hold, fortification, or Armor. doun, deep, or Ir. dûn, fortified hill, or Lat. domus (fortis), a (strong) house.]

1Sense 1. The innermost keep or strongest tower of a castle; donjon.

2Sense 2. A secure prison; especially, a dark, subterranean place of confinement. “To enter into so foul a dungeon.” Chaucer.

Year after year he lay patiently in a dungeon. Macaulay.