dungeon

Concise Oxford English Dictionary © 2008 Oxford University Press:
dungeon/ˈdʌnʤən/

▶noun

• 1 a strong underground prison cell, especially in a castle.

• 2 archaic term for donjon.

▶verb literary imprison in a dungeon.

– origin ME: from OFr. (perh. orig. with the sense ‘lord's tower’), based on L. dominus ‘lord’.