Definition from Wiktionary, the free dictionary
From Latin for "membrane around a fetus", from Greek "bowl in which the blood of victims was caught", from ame, (bucket)
- (anatomy) the innermost membrane of the fetal membranes of reptiles, birds, and mammals; the sac in which the embryo is suspended.
Derived terms 
innermost membrane of the fetal membranes of reptiles, birds, and mammals
- accusative singular of amnio