noun pl. amnions -·ni·ons or amnia -·nia (-ə)

1. the innermost membrane of the sac enclosing the embryo of a mammal, reptile, or bird: it is filled with a watery fluid (amniotic fluid)
2. a similar membrane of certain invertebrates, esp. insects

Etymology: Gr, dim. of amnos, lamb < IE *agwhnos > yean, L agnus