The Collaborative International Dictionary of English v.0.48:

dibutyl \di*bu"tyl\ (d[-i]*b[=u]"t[i^]l), n. [Pref. di- +
   butyl.] (Chem.)
   A liquid hydrocarbon, C8H18, of the alkane series, being
   one of several octanes, and consisting of two butyl radicals.
   Cf. Octane.
   [1913 Webster]