Definition of amnion in English:


Syllabification: am·ni·on
Pronunciation: /ˈamnēˌän, -ən

noun (plural - or amnionia /-nēə/)

The innermost membrane that encloses the embryo of a mammal, bird, or reptile.
More example sentences
  • Inside the egg are a series of fluid-filled membranes which permit the embryo to survive: the amnion, allantois, yolk sac, and chorion.
  • The middle part of the streak gives rise mainly to lateral plate mesoderm, while the posterior part of the streak provides the extra-embryonic mesoderm of the amnion, visceral yolk sac, and allantois.
  • We're talking about things like the amnion, the chorion, the allantoic sac, the placenta, the umbilical cord, if those words sound familiar to you.


mid 17th century: from Greek, 'caul', diminutive of amnos 'lamb'.



Pronunciation: /ˌamnēˈätik/
More example sentences
  • Many of the studies arising from his work on insects and amniotic vertebrates are cited below.
  • The fetus floats in amniotic fluid inside the amniotic sac.
  • In the second pregnancy trimester abnormal amniotic fetal cells can be detected.

Definition of amnion in:

Get more from Oxford Dictionaries

Subscribe to remove adverts and access premium resources

Word of the day demoralize
Pronunciation: dɪˈmɒrəlʌɪz
cause (someone) to lose confidence or hope