pyx·id·i·um \pikˈsidēəm\noun (pluralpyxid·ia \-ēə\ ; orpyxidiums) Etymology: New Latin, from Greek pyxidion, diminutive of pyxis box 1.: a capsular fruit (as in the plantain) that dehisces around its circumference so that the upper portion falls off like a cap — compare circumscissile 2.: capsule 2b