noun. the outermost membranous sac enclosing the embryo in higher vertebrates (reptiles, birds and mammals).
- fetal membrane
- chorionic villus
- chorion (Latin)
- χοριον (Ancient Greek (to 1453))
Example sentences of the word chorion
1. Noun, singular or mass
Each egg is surrounded by a chorion, a hard outer shell that protects the larva.