The word "endodermic" refers to the innermost layer of cells in an embryo that eventually give rise to the respiratory and digestive organs. Some synonyms for this term include endodermal, endodermous, and endodermatous. Other related terms include ectodermic, which refers to the outermost layer of cells in an embryo that give rise to the skin and nervous system, and mesodermic, which refers to the middle layer of cells that give rise to the muscles, bones, and circulatory system. Understanding these different layers is important in the study of embryology and developmental biology.