The Collaborative International Dictionary of English v.0.48:

Dibasic \Di*ba"sic\, a. [Pref. di- + basic.] (Chem.)
   Having two acid hydrogen atoms capable of replacement by
   basic atoms or radicals, in forming salts; bibasic; -- said
   of acids, as oxalic or sulphuric acids. Cf. Diacid,
   Bibasic.
   [1913 Webster]

   Note: In the case of certain acids dibasic and divalent are
         not synonymous; as, tartaric acid is tetravalent and
         dibasic, lactic acid is divalent but monobasic.
         [1913 Webster]