oubliette

A dungeon with a trapdoor in the ceiling as its only means of entrance or exit.

To imprison in an oubliette.

A secret dungeon with an opening only at the top for the admission of air, used for persons condemned to perpetual imprisonment or to perish secretly, such as exist in some old castles or other buildings.

A secret pit, usually in the floor of a dungeon or a dark passage, into which a person could be precipitated and thus be destroyed unawares.

A dungeon with an opening only at the top, found in some old castles and other strongholds, into which persons condemned to perpetual imprisonment, or to perish secretly, were thrust, or lured to fall.

a dungeon with the only entrance or exit being a trap door in the ceiling