[am.ni.on] n, pl amnions or am.nia [NL, fr. Gk, caul, fr. amnos lamb--more at yean] (1667) 1: a thin membrane forming a closed sac about the embryos of reptiles, birds, and mammals and containing a serous fluid in which the embryo is immersed
2: a membrane analogous to the amnion and occurring in various invertebrates -- am.ni.ot.ic adj