Source : Webster's Revised Unabridged Dictionary (1913)

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

Brig \Brig\ (br[i^]g), n.
   A bridge. [Scot.] --Burns.

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

   {Hermaphrodite brig}, a two-masted vessel square-rigged
      forward and schooner-rigged aft. See Illustration in
      Appendix.

Source : WordNet®

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