The Collaborative International Dictionary of English v.0.48:

Barn \Barn\ (b[aum]rn), n. [OE. bern, AS. berern, bern; bere
   barley + ern, [ae]rn, a close place. [root]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.
   [1913 Webster]

   Barn owl (Zool.), an owl of Europe and America (Aluco
      flammeus, or Strix flammea), which frequents barns and
      other buildings.

   Barn swallow (Zool.), the common American swallow (Hirundo
      horreorum), which attaches its nest of mud to the beams
      and rafters of barns.
      [1913 Webster]

WordNet (r) 3.0 (2006):

barn swallow
    n 1: common swallow of North America and Europe that nests in
         barns etc. [syn: barn swallow, chimney swallow,
         Hirundo rustica]