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.