Source : Webster's Revised Unabridged Dictionary (1913)

Barn \Barn\, n. [OE. bern, AS. berern, bern; bere barley + ern,
   [ae]rn, a close place. ?92. See {Barley}.]
   A covered building used chiefly for storing grain, hay, and
   other productions of a farm. In the United States a part of
   the barn is often used for stables.

   {Barn owl} (Zo["o]l.), an owl of Europe and America ({Aluco
      flammeus}, or {Strix flammea}), which frequents barns and
      other buildings.

   {Barn swallow} (Zo["o]l.), the common American swallow
      ({Hirundo horreorum}), which attaches its nest of mud to
      the beams and rafters of barns.

Barn \Barn\, v. t.
   To lay up in a barn. [Obs.] --Shak.

         Men . . . often barn up the chaff, and burn up the
         grain.                                   --Fuller.

Barn \Barn\, n.
   A child. [Obs.] See {Bairn}.

Source : WordNet®

barn
     n 1: an outlying farm building for storing grain or animal feed
          and housing farm animals
     2: (physics) a unit of nuclear cross section; the effective
        circular area that one particle presents to another as a
        target for an encounter [syn: {b}]