endothelium

noun, plural en·do·the·li·a [en-doh-thee-lee-uh] /ˌɛn doʊˈθi li ə/.

1. a type of epithelium composed of a single layer of smooth, thin cells that lines the heart, blood vessels, lymphatics, and serous cavities.

noun plural -lia (-lɪə)

1. a tissue consisting of a single layer of cells that lines the blood and lymph vessels, heart, and some other cavities

n. pl. en•do•the•li•a (-lē-ə)

1. A thin layer of flat epithelial cells that lines serous cavities, lymph vessels, and blood vessels.

Plural endothelia

1. A thin layer of flat epithelial cells that lines the lymph vessels, blood vessels, and the inner cavities of the heart. Compare mesothelium.