the.com/brig

means A prison cell aboard a ship (and by extension, naval slang for any jail or lockup).

from Short for 'brigantine,' a two-masted sailing ship — the word narrowed to mean 'ship's jail' because brigantines were commonly used in navies as vessels for holding prisoners, and the lockup aboard such ships became known simply as 'the brig.' The sense stuck even after the ship type faded from use.