Source : Webster's Revised Unabridged Dictionary (1913)

Basidium \Ba*sid"i*um\, n. [NL., dim. of Gr. ? base.] (Bot.)
   A special oblong or pyriform cell, with slender branches,
   which bears the spores in that division of fungi called
   Basidiomycetes, of which the common mushroom is an example.

Source : WordNet®

basidium
     n : a small club-shaped structure typically bearing four
         basidiospores at the ends of minute projections; unique
         to basidiomycetes
     [also: {basidia} (pl)]