The Collaborative International Dictionary of English v.0.48:

dicarbonic \di`car*bon"ic\ (d[imac]`k[aum]r*b[o^]n"[i^]k), a.
   [Pref. di- + carbonic.] (Chem.)
   Containing two carbon residues, or two carboxyl groups or
   radicals; as, oxalic acid is the simplest dicarbonic acid. In
   the latter sense, synonymous with dicarboxylic; as,
   succinic acid is a dicarboxylic acid.
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

dicarboxylic
    adj 1: containing two carboxyls per molecule