1. A large building for sheltering livestock, storing hay or other agricultural products, or housing equipment used for operating a farm.
2. A large shed for the housing of vehicles, such as railroad cars.
3. A particularly large, typically bare building: lived in a barn of a country house.
4. Abbr. b Physics A unit of area equal to 10-24 square centimeters, used to measure cross sections in nuclear physics.
[Middle English bern, from Old English berærn : bere, barley; see bhares- in the Appendix of Indo-European roots + ærn, house.]
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