The Collaborative International Dictionary of English v.0.48:

Meconic \Me*con"ic\, a. [Gr. ? belonging to the poppy, fr. ? the
   poppy: cf. F. m['e]conique.]
   Pertaining to, or obtained from, the poppy or opium; specif.
   (Chem.), designating an acid related to aconitic acid, found
   in opium and extracted as a white crystalline substance.
   [1913 Webster]