promethium

n. rare metallic element (Chemistry)

Promethium (IPA: ) is a chemical element in the periodic table that has the symbol Pm and atomic number 61. It is notable for being the only other radioactive element besides technetium which is followed by chemical elements that have stable isotopes.
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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
(synonym) Pm, atomic number 61
(hypernym) metallic element, metal

n. promethium, rare metallic element (Chemistry)

n. (also: Pm) promethium, lanthanide rare earth element