Diacid

from The Collaborative International Dictionary of English v.0.48

Diacid \Di*ac"id\, a. [Pref. di- + acid.] (Chem.)
   Divalent; -- said of a base or radical as capable of
   saturating two acid monad radicals or a dibasic acid. Cf.
   {Dibasic}, a., and {Biacid}.
   [1913 Webster]