n. pl. em·bry·os 1. a. The collection of cells that has developed from the fertilized egg of a vertebrate animal, before all the major organs have developed.
b. A collection of such cells of a human, especially from implantation in the uterine wall through the eighth week of development.
2. Botany The young sporophytic plant contained within a seed or an archegonium.
3. An organism at any time before full development, birth, or hatching.
4. A rudimentary or beginning stage: an idea that was the embryo of a short story.