ˈamnēˌän, -_ən noun
( plural amnions -nz ; or am·nia -ēə)
Etymology: New Latin, from Greek, caul, probably from diminutive of amnos lamb — more at yean
1. : a thin membranous fluid-filled sac surrounding the embryo (of reptile, bird, or mammal) that is typically formed together with the chorion through growth about the embryo of the amniotic folds, these folds completely enclosing the embryo, fusing at their line of final contact, and then splitting across the line of fusion to separate an inner amnion immediately enclosing the embryo and an outer chorion
2. : a membrane resembling an amnion and enclosing the embryos of many insects and other invertebrates