amniotic sac amniotic fluid • amniotitis · · · Info · Definitions · Synonyms · Characters · · amniotic sac · · Text Common · · Latin · · Scripts 12 · · Length 4 · · Syllables Definitions · · · (noun) thin innermost membranous sac enclosing the developing embryo of higher vertebrates (reptiles, birds and mammals). Synonyms: amnion, amniotic sac, amnios. · · Noun Definition 1 Synonyms · · · amnion · · Synonym 1 amnios · · Synonym 2 Characters · · space U+0020 a latin small letter a U+0061 c latin small letter c U+0063 i latin small letter i U+0069 m latin small letter m U+006D n latin small letter n U+006E o latin small letter o U+006F s latin small letter s U+0073 t latin small letter t U+0074