atomic number 91 atomic number 90 • atomic number 92 · · · Info · Definitions · Synonyms · Characters · · atomic number 91 · · Text Common · · Latin · · Scripts 16 · · Length 9 · · Syllables Definitions · · · (noun) a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead. Synonyms: protactinium, protoactinium, Pa, atomic number 91. · · Noun Definition 1 Synonyms · · · protactinium · · Synonym 1 protoactinium · · Synonym 2 pa · · Synonym 3 Characters · · space U+0020 1 digit one U+0031 9 digit nine U+0039 a latin small letter a U+0061 b latin small letter b U+0062 c latin small letter c U+0063 e latin small letter e U+0065 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 r latin small letter r U+0072 t latin small letter t U+0074 u latin small letter u U+0075