amnion

[am-nee-uhn]
noun, plural amnions, amnia [am-nee-uh] .
1.
Anatomy, Zoology. the innermost of the embryonic or fetal membranes of reptiles, birds, and mammals; the sac in which the embryo is suspended.
2.
Zoology. a similar membrane of insects and other invertebrates.

Origin:
1660–70; < Greek, equivalent to amn(ós) lamb (see yean) + -ion diminutive suffix

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World English Dictionary
amnion (ˈæmnɪən)
 
n , pl -nions, -nia
See also chorion the innermost of two membranes enclosing an embryonic reptile, bird, or mammal
 
[C17: via New Latin from Greek: a little lamb, from amnos a lamb]

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Etymonline
Word Origin & History

amnion
1660s; see amniotic.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

amnion am·ni·on (ām'nē-ən, -ŏn')
n. am·ni·ons or am·ni·a (-nē-ə)
The thin, membranous sac filled with a serous fluid in which the embryo or fetus is enclosed and suspended in the uterus. Also called amniotic sac.


am'ni·ot'ic (-ŏt'ĭk) or am'ni·on'ic (-ŏn'ĭk) adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
amnion   (ām'nē-ən)  Pronunciation Key 
A thin, membranous sac filled with a watery fluid (called the amniotic fluid) in which the embryo or fetus of a reptile, bird, or mammal is suspended during prenatal development. Also called amniotic sac.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica
Encyclopedia

amnion

in reptiles, birds, and mammals, a membrane forming a fluid-filled cavity (the amniotic sac) that encloses the embryo. The amniotic sac and the fluid it contains are sometimes referred to as the bag of waters

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
Amniotic constriction bands are caused by damage to a part of the placenta called the amnion.
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