[ am-nee-uhn ]
See synonyms for amnion on
noun,plural am·ni·ons, am·ni·a [am-nee-uh]. /ˈæm ni ə/.
  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 of amnion

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

Words Nearby amnion Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use amnion in a sentence

British Dictionary definitions for amnion


/ (ˈæmnɪən) /

nounplural -nions or -nia (-nɪə)
  1. the innermost of two membranes enclosing an embryonic reptile, bird, or mammal: See also chorion

Origin of amnion

C17: via New Latin from Greek: a little lamb, from amnos a lamb

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for amnion


[ ămnē-ən ]

  1. 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 © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.