Chorion

Part of speech: noun

Pronunciation: /ˈkɔɹiɑn/

Definitions

1. a membrane surrounding the fetus in mammals that forms part of the placenta and aids in nutrient exchange
2. the outermost embryonic membrane in vertebrates that contributes to placental development and fetal nutrition
3. a protective fetal membrane in mammals that participates in placental formation and provides nutritional support to the developing organism

Etymology: The membrane that wraps a developing embryo has a name that goes back to ancient Greek medicine, where "khórion" referred to the membrane surrounding the fetus and to the afterbirth. The Greek word passed into Late Latin as "chorion," and English later took it up as a technical term for that outermost fetal layer. The word's history stays close to its original meaning, with no dramatic shift. What changed is the setting: a term used in Greek and Latin medical writing became a precise anatomical label, used in modern embryology to pick out one of the membranes that surround the developing young of mammals, birds and reptiles.