Oubliette, n.

Oubliette (o͞o-ble-ĕt'), n. [Fr., from oublier, to forget, Pr. & O. Sp. oblidar, It. obbliare, N. Sp. olvidar, Lat. oblivisci, oblitus.] A dungeon with an opening only at the top, for persons condemned to perpetual imprisonment, or to perish secretly.

The place was utterly dark, the oubliette, I suppose, of the accursed convent. W. Scott.