The Collaborative International Dictionary of English v.0.48:

Brig \Brig\, n.
   A bridge. [Scot.] --Burns.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Brig \Brig\, n. [Shortened from Brigantine.] (Naut.)
   A two-masted, square-rigged vessel.
   [1913 Webster]

   Hermaphrodite brig, a two-masted vessel square-rigged
      forward and schooner-rigged aft. See Illustration in
      Appendix.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Brig \Brig\, n. [Origin unknown.] (Nav.)
   On a United States man-of-war, the prison or place of
   confinement for offenders.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

brig
    n 1: two-masted sailing vessel square-rigged on both masts
    2: a penal institution (especially on board a ship)

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "brig":
   POW camp, bastille, black hole, borstal, borstal institution,
   bridewell, calaboose, can, cell, clink, concentration camp,
   condemned cell, cooler, death cell, death house, death row,
   detention camp, federal prison, forced-labor camp, gaol,
   guardhouse, guardroom, house of correction, house of detention,
   industrial school, internment camp, jail, jailhouse, keep,
   labor camp, lockup, maximum-security prison,
   minimum-security prison, oubliette, pen, penal colony,
   penal institution, penal settlement, penitentiary, prison,
   prison camp, prisonhouse, reform school, reformatory,
   sponging house, state prison, stockade, the hole, tollbooth,
   training school