epithelium

epiteelikudos, epiteeli puhekieltä 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.
1969, Vladimir Nabokov, Ada or Ardor, Penguin 2011, p. 25:

the passenger's roving eyes paused for a moment as he listened inwardly to a nether itch, which he supposed to be (correctly, thank Log) only a minor irritation of the epithelium.