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Definition of: amnion
(am′nē·ən) noun plural ·ni·ons or ·ni·a (-nē·ə)
A tough, membranous, fluid-containing sac enclosing the embryo of birds, reptiles, and mammals. [<Gk. amnion the fetal envelope, dim. of amnos lamb]
—am·ni·on·ic (am′nē·on′ik), am·ni·ot·ic (am′nē·ot′ik) adjective
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