epithelium(n = noun.body) epithelial tissue - membranous tissue covering internal organs and other internal surfaces of the body;
is a kind of animal tissue
has parts: epithelial cell
has particulars: endothelium, mesothelium, neuroepithelium, decidua
Derived form adjective epithelial₁

   The superficial layer of cells lining the alimentary canal and all its appendages, all glands and their ducts, blood vessels and lymphatics, serous cavities, etc. It often includes the epidermis (i. e., keratin-producing epithelial cells), and it is sometimes restricted to the alimentary canal, the glands and their appendages, -- the term endothelium being applied to the lining membrane of the blood vessels, lymphatics, and serous cavities. [1913 Webster]

epithelium, n. (pl. epitheliums or epithelia) the tissue forming the outer layer of the body surface and lining many hollow structures.

Derivative:
epithelial adj.

Etymology:
mod.L f. EPI- + Gk thele teat