An Etymological Dictionary of Astronomy and Astrophysics
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Artificially produced radioactive chemical element; symbol Pm, the last of the rare-earths family elements to be discovered. Atomic number 61; mass number of most stable isotope 145; melting point 1,042°C; boiling point 3,000°C.

From → Prometheus. The name promethium was preferred to prometheum because most metallic elements have names ending in ium and eum would have caused problems.