/ Dictionary / Index E endothelium: Meaning and Definition of Find definitions for: en•do•the•li•um Pronunciation: (en"dō-thē'lē-um), [key] — pl. -li•a a type of epithelium composed of a single layer of smooth, thin cells that lines the heart, blood vessels, lymphatics, and serous cavities. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: endothelium (Thesaurus) endothelioma endotherm Related Content Daily Word Quiz: soporific Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language