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]

The Collaborative International Dictionary of English v.0.48:

Barn \Barn\, v. t.
   To lay up in a barn. [Obs.] --Shak.
   [1913 Webster]

         Men . . . often barn up the chaff, and burn up the
         grain.                                   --Fuller.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Barn \Barn\, n.
   A child. See Bairn. [Obs.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

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: barn, b]

The Jargon File (version 4.4.7, 29 Dec 2003):

barn
 n.

    [uncommon; prob. from the nuclear military] An unexpectedly large quantity
    of something: a unit of measurement. ?Why is /var/adm taking up so much
    space?? ?The logs have grown to several barns.? The source of this is
    clear: when physicists were first studying nuclear interactions, the
    probability was thought to be proportional to the cross-sectional area of
    the nucleus (this probability is still called the cross-section). Upon
    experimenting, they discovered the interactions were far more probable than
    expected; the nuclei were ?as big as a barn?. The units for cross-sections
    were christened Barns, (10^-24 cm^2) and the book containing cross-sections
    has a picture of a barn on the cover.


Easton's 1897 Bible Dictionary:

Barn
   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).


Bouvier's Law Dictionary, Revised 6th Ed (1856):

BARN, estates. A building on a farm used to receive the crop, the stabling
of animals, and other purposes.
     2. The grant or demise of a barn, without words superadded to extend
its meaning, would pass no more than the barn itself, and as much land as
would be necessary for its complete enjoyment. 4 Serg. & Rawle, 342.