/ˌepəˈTHēlēəm/
Noun, pl. epithelia
1. One of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective absorption, protection, transcellular transport and detection of sensation. (wikipedia.org)
2. A membranous tissue composed of one or more layers of cells which forms the covering of most internal and external surfaces of the body and its organs: internally including the lining of vessels and other small cavities, and externally being the skin. (wiktionary.org)
3. The thin tissue forming the outer layer of a body’s surface and lining the alimentary canal and other hollow structures. (Google Dictionary)
4. More specifically, the part of this derived from embryonic ectoderm and endoderm, as distinct from endothelium and mesothelium. (Google Dictionary)
Syn: Epithelial tissue
Word origin: Modern Latin epithēlium, from Ancient Greek ἐπί (epi, “on, atop, epi-”) + θηλή (thēlē, “nipple”).