epithelium

noun

1. (countable, uncountable)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.

   “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.”

   “The sap of this species was able to cause loss of corneal epithelium 16 h after direct exposure to the sap in a 60-year-old male.”