epithelium

Concise Oxford English Dictionary © 2008 Oxford University Press:
epithelium /ˌɛpɪˈθiːlɪəm/

▶noun (pl. epithelia /-lɪə/) Anatomy the thin tissue forming the outer layer of the body's surface and lining the alimentary canal and other hollow structures, especially that part derived from the embryonic ectoderm and endoderm. Compare with endothelium.

– derivatives
epithelial adjective.

– origin C18: mod. L., from epi- + Gk thēlē ‘teat’.