Source : Webster's Revised Unabridged Dictionary (1913)

Oospore \O"["o]*spore\, n. [Gr. ? an egg + ? a seed.] (Bot.)
   (a) A special kind of spore resulting from the fertilization
       of an o["o]sphere by antherozoids.
   (b) A fertilized o["o]sphere in the ovule of a flowering
       plant.

Source : WordNet®

oospore
     n : a thick-walled sexual spore that develops from a fertilized
         oosphere in some algae and fungi