Embryos are the earliest stage of development in many organisms, including humans. While the term "embryo" is commonly used in biology and medicine, there are several synonyms that can also be used to describe this stage of development. Some common synonyms for "embryo" include "zygote," which refers to the single cell that forms when an egg is fertilized, "blastula," which is the hollow ball of cells that forms after the zygote undergoes several rounds of cell division, and "gastrula," which is the stage where the embryo begins to differentiate into different layers of tissues. Using different synonyms for "embryo" can help to add variety and depth to scientific writing and discussions.