1900, in the meaning defined above
borrowed from French, from Greek aktīn-, aktís "ray, beam" + -ium -ium; so called from its radioactivity — more at actin-
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“Actinium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/actinium. Accessed 28 Feb. 2021.
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