from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. Alternative form of protactinium. (dated)

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead


Sorry, no etymologies found.


  • Thus were found the mesothorium now used by physicians and manufactured industrially, radio-thorium, ionium, protoactinium, radio-lead, and other substances.

    Pierre Curie

  • That's radioactive, but it takes two million years before it becomes protoactinium, which changes to uranium in twenty-seven days, which changes to thorium after a hundred and sixty thousand years, which changes to radium, then to actinium, then to -- "

    Asimov's Science Fiction


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