Webster's Revised Unabridged Dictionary · 1913

dungeon

dungeon (dun"jun) , noun

[Old English donjoun highest tower of a castle, tower, prison, French donjon tower or platform in the midst of a castle, turret, or closet on the top of a house, a keep of a castle, Late Latin domnio, the same word as Late Latin dominus lord. See Dame, Don, and compare Dominion, Domain, Demesne, Danger, Donjon.]

A close, dark prison, commonly, under ground, as if the lower apartments of the donjon or keep of a castle, these being used as prisons.
Down with him even into the deep dungeon. — Tyndale
Year after year he lay patiently in a dungeon. — Macaulay

Dungeon , transitive verb

To shut up in a dungeon. — Bp. Hall