The Collaborative International Dictionary of English v.0.48:

Leuconic \Leu*con"ic\ (-k[o^]n"[i^]k), a. [Leuc- + croconic.]
   (Chem.)
   Pertaining to, or designating, a complex organic acid,
   obtained as a yellowish white gum by the oxidation of
   croconic acid.
   [1913 Webster]