\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.