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- 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.
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 -- "