|  b 
  
 
 1. (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
 • Topics:
 nuclear physics, atomic physics, nucleonics
 • Hypernyms:
 area unit, square measure
 2. the 2nd letter of the Roman alphabet
 • Syn:
 B
 • Hypernyms:
 letter, letter of the alphabet, alphabetic character
 • Member Holonyms:
 Roman alphabet, Latin alphabet
 
 
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