Greek ἀμνίον (amnion), from amnion (amnion)
“amnion,” “membrane,” “membrane surrounding the fetus”
The word entered English in the 1640s as amnion (noun), borrowed from Late Latin amnion, from Greek amnion — literally “membrane.” The root amnion (“membrane”) connects amnio- to the entire embryonic membranes: amniocentesis (amnio- + kentein → puncture of the amnion), amniotomy (amnio- + tome → incision into the amnion), and amniotic (pertaining to the amnion). The combining formamnio- is highly productive in obstetrics and embryology: e.g., amniochoreosis, amniopathy, and amniochorion.