OospereO"["o]*spere\, n. [Gr. ? an egg + E. sphere.]1. (Bot.) An unfertilized, rounded mass of protoplasm, produced in an o["o]gonium. Note: After being fertilized by the access of antherozoids it becomes covered with a cell wall and develops into an o["o]spore, which may grow into a new plant like the parent. 2. (Bot.) An analogous mass of protoplasm in the ovule of a flowering plant; an embryonic vesicle. --Goodale.