promethium Prometheus • promic · · · Info · Definitions · Synonyms · Characters · · promethium · · Text Latin · · Script 10 · · Length Definitions · · · (noun) a soft silvery metallic element of the rare earth group having no stable isotope; was discovered in radioactive form as a fission product of uranium. Synonyms: Pm, atomic number 61. · · Noun Definition 1 Synonyms · · · pm · · Synonym 1 atomic number 61 · · Synonym 2 Characters · · e latin small letter e U+0065 h latin small letter h U+0068 i latin small letter i U+0069 m latin small letter m U+006D o latin small letter o U+006F p latin small letter p U+0070 r latin small letter r U+0072 t latin small letter t U+0074 u latin small letter u U+0075