promethium

Noun
  1. 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 (synset 114675658)
    is a type of: metal, metallic element - any of several chemical elements that are usually shiny solids that conduct heat or electricity and can be formed into sheets etc.
    same as: atomic number 61, pm

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