The Collaborative International Dictionary of English v.0.48:
Amnios \Am"ni*os\, n. Same as Amnion. [1913 Webster]WordNet (r) 3.0 (2006):
amnios n 1: thin innermost membranous sac enclosing the developing embryo of higher vertebrates (reptiles, birds and mammals) [syn: amnion, amniotic sac, amnios]