Source : Webster's Revised Unabridged Dictionary (1913)

Pyxidium \Pyx*id"i*um\, n.; pl. {Pyxidia}. [NL., fr. Gr. ?, dim.
   a ? a box. See {Pyx}.] (Bot.)
   (a) A pod which divides circularly into an upper and lower
       half, of which the former acts as a kind of lid, as in
       the pimpernel and purslane.
   (b) The theca of mosses.

Source : WordNet®

pyxidium
     n : fruit of such plants as the plantain; a capsule whose upper
         part falls off when the seeds are released [syn: {pyxis}]
     [also: {pyxidia} (pl)]