The Collaborative International Dictionary of English v.0.48:

Meconin \Mec"o*nin\, n. [Cf. F. m['e]conine.] (Chem.)
   A substance regarded as an anhydride of meconinic acid,
   existing in opium and extracted as a white crystalline
   substance. Also erroneously called meconina, meconia,
   etc., as though it were an alkaloid.
   [1913 Webster]