a dark cell (usually underground) where prisoners can be confined
"The brave knight managed to escape from the damp dungeon before the guards could return."
An underground prison or vault, typically built underneath a castle.
"The brave knight descended into the damp dungeon beneath the ancient castle to rescue his captured friend."
In plain English: A dungeon is a dark, underground cell where prisoners are kept locked up for punishment or safety.
"The old castle had many dark dungeons where prisoners were kept."
Usage: The term is often used metaphorically to describe any dark, oppressive place of confinement rather than strictly an underground cell. Avoid using "dungeon" as a verb in modern casual speech; the phrasal construction "lock up in a dungeon" sounds more natural.
To imprison in a dungeon.
"The villain was dungeoned until he confessed his crimes."
From Middle English dongeoun ("keep of a castle; dungeon; abyss, cave, den; whirlpool"), from Anglo-Norman donjun ("keep of a castle; keep used as a prison; dungeon") and continental Old French donjon ("keep of a castle"), from Vulgar Latin *dominiōnem, seemingly derived from Latin dominus ("master, lord") perhaps via some figurative sense like "dominant building". Doublet of donjon. The sense of "prison (associated with a castle)", first attested in Anglo-Norman (13th c.