Source : Webster's Revised Unabridged Dictionary (1913)

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}.