epithelium

noun

ep·​i·​the·​li·​um ˌe-pə-ˈthē-lē-əm 

plural epithelia ˌe-pə-ˈthē-lē-ə 

1

: a membranous cellular tissue that covers a free surface or lines a tube or cavity of an animal body and serves especially to enclose and protect the other parts of the body, to produce secretions and excretions, and to function in assimilation

2

: a usually thin layer of parenchyma that lines a cavity or tube of a plant

Examples of epithelium in a Sentence

Recent Examples on the Web

Unlike skin, which acts as a tight physical barrier, the junctional epithelium is naturally porous. —New Atlas, 9 Aug. 2025

These issues can include: Corneal abrasions: Contact lenses or foreign objects can scratch or scrape the epithelium, the outer layer of your cornea. —Anna Giorgi, Verywell Health, 1 Aug. 2025

The deep tissues between your tooth and gums lack the same protection that other epithelia have. —Monica Cull, Discover Magazine, 29 July 2025

Two light microscope images representing the junctional epithelium. —Hannah Millington, MSNBC Newsweek, 30 July 2025

Word History

Etymology

New Latin, from epi- + Greek thēlē nipple — more at feminine

First Known Use

1748, in the meaning defined at sense 1

Kids Definition

epithelium

noun

ep·​i·​the·​li·​um ˌep-ə-ˈthē-lē-əm 

plural epithelia -lē-ə 

1

: a tissue like a membrane that is made up of cells and covers a free surface or lines a tube or cavity of an animal body

2

: a usually thin layer of cells of a plant that is part of the parenchyma and lines a cavity or tube

epithelial

-lē-əl

adjective

Medical Definition

epithelium

noun

ep·​i·​the·​li·​um ˌep-ə-ˈthē-lē-əm 

plural epithelia -lē-ə 

: a membranous cellular tissue that covers a free surface or lines a tube or cavity of an animal body and serves especially to enclose and protect the other parts of the body, to produce secretions and excretions, and to function in assimilation