ionium Hear it!

ionium definition

io·ni·um (ī ō′nē əm)

noun

a radioactive isotope of thorium having a mass number of 230 and a half-life of 8 × 10 years

Etymology: ion + -ium

Webster's New World College Dictionary Copyright © 2009 by Wiley Publishing, Inc., Cleveland, Ohio.
Used by arrangement with John Wiley & Sons, Inc.

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