What does "amnion" mean?

The innermost membrane of the fetal membranes of reptiles, birds, and mammals; the sac in which the embryo is suspended.

Amnion

Common synonyms include: amnios, amniotic sac, allantoic membrane, amniotic sac, anatomy, arachnoid membrane.

//ˈæm.nɪ.ɒn// noun

noun ·Uncommon ·Advanced level

Noun

1
The innermost membrane of the fetal membranes of reptiles, birds, and mammals; the sac in which the embryo is suspended.
"Near-synonym: amniotic sac"
2
thin innermost membranous sac enclosing the developing embryo of higher vertebrates (reptiles, birds and mammals) wordnet

"He never seemed to mind, and after a while, she no longer felt self-conscious about languishing in the amnion of his office."

From Latin amnion (“membrane around a fetus”), from Ancient Greek ἀμνίον (amníon).

Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.