From physics, a unit of area equal to 10^-24 square centimeter. Used to measure collision cross sections.

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.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.

Barn (?), n. [OE. bern, AS. berern, bern; bere barley + ern, aern, 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 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.

© Webster 1913.

Barn, v. t.

To lay up in a barn.

Shak.

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

© Webster 1913.

Barn, n.

A child. [Obs.] See Bairn.

© Webster 1913.