ec·to·derm / ˈektəˌdərm/ • n. Zool. & Embryology the outermost layer of cells or tissue of an embryo in early development, or the parts derived from this, which include the epidermis, nerve tissue, and nephridia. Compare with endoderm and mesoderm.DERIVATIVES: ec·to·der·mal / ˌektōˈdərməl/ adj.

ectoderm In a triploblastic embryo, the outer layer of cells which eventually give rise to the epidermis, the most anterior and posterior portions of the digestive tract, and the majority of the nervous system.

ectoderm (ek-toh-derm) n. the outer of the three germ layers of the early embryo. It gives rise to the nervous system and sense organs, the teeth and lining of the mouth, and the epidermis and its associated structures (hair, nails, etc.).
—ectodermal adj.

ectoderm The external layer of cells of the gastrula, which will develop into the epidermis and the nervous system in the adult. See also germ layers.