/am"nee euhn/ , n. , pl. amnions, amnia /-nee euh/ .
1. Anat. , Zool. the innermost of the embryonic or fetal membranes of reptiles, birds, and mammals; the sac in which the embryo is suspended.
2. Zool. a similar membrane of insects and other invertebrates.
[ 1660-70; amn ( ós ) lamb (see YEAN) + -ion dim. suffix ]