From 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.