The Collaborative International Dictionary of English v.0.48:

Sporidium \Spo*rid"i*um\ (sp[-o]*r[i^]d"[i^]*[u^]m), n.; pl.
   Sporidia (-[.a]). [NL. See Spore.] (Bot.)
   (a) A secondary spore, or a filament produced from a spore,
       in certain kinds of minute fungi.
   (b) A spore.
       [1913 Webster]