Source : Webster's Revised Unabridged Dictionary (1913)

Archegonium \Ar`che*go"ni*um\, n. [NL., fr. Gr. ? the first of a
   race.] (Bot.)
   The pistillidium or female organ in the higher cryptogamic
   plants, corresponding to the pistil in flowering plants.

Source : WordNet®

archegonium
     n : a female sex organ occurring in mosses, ferns, and most
         gymnosperms
     [also: {archegonia} (pl)]