Source : Webster's Revised Unabridged Dictionary (1913)

   {Benzene nucleus}, {Benzene ring} (Chem.), a closed chain or
      ring, consisting of six carbon atoms, each with one
      hydrogen atom attached, regarded as the type from which
      the aromatic compounds are derived. This ring formula is
      provisionally accepted as representing the probable
      constitution of the benzene molecule, {C6H6}, and as the
      type on which its derivatives are formed.

Source : WordNet®

benzene nucleus
     n : a closed chain of 6 carbon atoms with hydrogen atoms
         attached [syn: {benzene formula}, {benzene ring}, {Kekule
         formula}]