# endothelium

> English word · Noun · frequency rank #68,192

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

## Etymology
From endo- + -thelium, as in epithelium.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/endothelium