amnion Meaning, Definition & Usage

  1. noun thin innermost membranous sac enclosing the developing embryo of higher vertebrates (reptiles, birds and mammals)
    amniotic sac; amnios.

WordNet

Am"ni*on noun
Etymology
Gr. the membrane round the fetus, dim. of lamb.
Definitions
  1. (Anat.) A thin membrane surrounding the embryos of mammals, birds, and reptiles.

Webster 1913