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

Barn
A country barn tells the story of its existence. Readers will learn about the barn and its many uses--including sheltering animals and serving as an antique shop--from the time it was raised in the late 18th century to the present day. Readers can also trace how historical events, such as the Great Depression and the Vietnam War, effected the barn. Illustrated with oil paintings

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1. \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.
   

2. \Barn\, v. t.
   To lay up in a barn. [Obs.] --Shak.
         Men . . . often barn up the chaff, and burn up the
         grain.                                   --Fuller.
   

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

a storehouse (Deut. 28:8; Job 39:12; Hag. 2:19) for grain, which was usually under ground, although also sometimes above ground (Luke 12:18).