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)