| NOUN | substance | atomic number 61, promethium, Pm | a soft silvery metallic element of the rare earth group having no stable isotope |
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| Meaning | 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. | |
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| Synonyms | promethium, Pm | |
| Broader | metallic element, metal | Any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc. |