The Collaborative International Dictionary of English v.0.48:

Diphenyl \Di*phe"nyl\, n. [Pref. di- + phenyl.] (Chem.)
   A white crystalline substance, C6H5.C6H5, obtained by
   leading benzene through a heated iron tube. It consists of
   two benzene or phenyl radicals united.
   [1913 Webster]