noun.
In anatomy, the superficial layer of cells of mucous membranes, covering the connective-tissue layer, corresponding to the epidermis of the outer skin and continuous with it at the mouth and other natural openings.
noun.
In ornithology, specifically, the dense, tough cuticular lining of the gizzard. It is sometimes even bony, and sometimes deciduous.
noun.
In botany, a delicate layer of cells lining the internal cavities of certain organs, as the young ovary, etc.: also applied to the thin epidermis of petals.