Source : Webster's Revised Unabridged Dictionary (1913)

Hymenium \Hy*me"ni*um\, n.; pl. L. {Hymenia}, E. {Hymeniums}.
   [NL., fr. Gr. ? a membrane.] (Bot.)
   The spore-bearing surface of certain fungi, as that on the
   gills of a mushroom.

Source : WordNet®

hymenium
     n : spore-bearing layer of cells in certain fungi containing
         asci or basidia
     [also: {hyniums} (pl), {hynia} (pl)]