Green’s Dictionary of Slang

1. (US black) a gun.

1931

S. Brown ‘Slow Coon’ in Botkin Folk-Say 118: Big Pete was a six-foot, Hardboiled man, Wid a forty-four dungeon In his han’ [...] ‘Don’t ’low no slow nigger Stay roun’ hyeah. I plugs ’em wid my dungeon.’.

2. (US teen) school.

1958

Times (Munster, IN) 19 Jan. 56/1: Slang keeps changing to keep up [...] ‘Dungeon’ — school.

3. (UK prison) an open area on the floor of a wing used for recreation, association etc.

1998

J. Hoskison Inside 40: The ‘dungeon’ was the dumping ground for lousy lunches and the occasional ‘shit parcel’.

4. (N.Z./US prison) a punishment/solitary confinement cell.

1922		O.F. Lewis Amer. Prisons and Prison Customs 223: [He] was put into the ‘dungeon’ and subjected to cruelties of treatment that horrified the State when published.
1999		D. Looser ‘Boob Jargon’ in NZEJ 13 29: dungeon n.Solitary confinement.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 63/1: dungeon n. the solitary confinement punishment cell.

5. a prison.

2007

C. Goffard Snitch Jacket 17: Six months in the dungeon, and what do I get? [...] just the fuckin’ stink-eye.