Source : Webster's Revised Unabridged Dictionary (1913)

Meconidium \Mec`o*nid"i*um\, n. [NL., dim. of Gr. ? a poppy. So
   called in allusion to the shape of the seed capsules of the
   poppy.] (Zo["o]l.)
   A kind of gonophore produced by hydroids of the genus
   {Gonothyr[ae]a}. It has tentacles, and otherwise resembles a
   free medusa, but remains attached by a pedicel.