ENDOTHELIUM
endothelium
(noun) an epithelium of mesoblastic origin; a thin layer of flattened cells that lines the inside of some body cavities
Source: WordNet® 3.1
Etymology
Noun
endothelium (plural endothelia)
(anatomy) A thin layer of flat epithelial cells that lines the heart, serous cavities, lymph vessels, and blood vessels.
Source: Wiktionary
En`do*the"li*um, n.; pl. Endothelia. Etym: [NL., fr. Gr. (Anat.)
Definition: The thin epithelium lining the blood vessels, lymphatics, and
serous cavities. See Epithelium.
Source: Webster’s Unabridged Dictionary 1913 Edition