"secret dungeon reached only via trapdoor and with an opening only at the top for admission of air," 1780, originally in a French context, from French oubliette (14c.), from oublier "to forget, show negligence" (Old French oblier, oblider), from Vulgar Latin *oblitare, from Latin oblitus, past participle of oblivisci "to forget" (see oblivion). Used for persons condemned to perpetual imprisonment or to perish secretly.
