The Collaborative International Dictionary of English v.0.48:

Diamine \Di*am"ine\ (?; 104), n. [Pref. di- + amine.] (Chem.)
   A compound containing two amido groups united with one or
   more basic or positive radicals, -- as contrasted with a
   diamide.
   [1913 Webster]

   Note: In chemical nomenclature, if any amine or diamine is
         named by prefixing the nitrogen group, the name of the
         latter takes the form of amido, diamido, etc., thus
         ethylene diamine, C2H4.(NH2)2, is also called
         diamido-ethylene.
         [1913 Webster]

WordNet (r) 3.0 (2006):

diamine
    n 1: any organic compound containing two amino groups