ˌepəˈthēlēəm noun
( plural epithe·lia -lēə ; also epitheliums )
Etymology: New Latin, from epi- + Greek thēlē nipple + New Latin -ium — more at feminine
1. : a cellular animal tissue that covers a free surface or lines a tube or cavity, that consists of one or more layers of cells forming a sheet practically unbroken by intercellular substance and either smoothly extended (as in epidermis) or much folded on a basement membrane and compacted (as in glands), and that serves especially to enclose and protect the other parts of the body, to form the most essential part of the sense organs, to produce secretions and excretions, and to function in assimilation — see endothelium
2. : any of certain layers of plant tissue one or more cells thick consisting of parenchyma that line an internal cavity or tube (as in a resin canal where they excrete the resin into the cavity)