amnion

UK: /ˈæmnɪən/ US: (am′nē ən)

Inflections of 'amnion' (n):

amnions

npl

amnia

npl

WordReference Random House Unabridged Dictionary of American English © 2026

am•ni•on  (am′nē ən), n., pl. -ni•ons, -ni•a 

(-nē ə). 
1. Anatomy the innermost of the embryonic or fetal membranes of reptiles, birds, and mammals;
   the sac in which the embryo is suspended.
2. [Zool.] a similar membrane of insects and other invertebrates.

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

Collins Concise English Dictionary © HarperCollins Publishers::

amnion / ˈæmnɪən/ noun ( -nions, -nia / -nɪə/)

1. the innermost of two membranes enclosing an embryonic reptile, bird, or mammal
   See also chorion

Etymology: 17th Century: via New Latin from Greek: a little lamb, from amnos a lamb