actinium

noun

ac·​tin·​i·​um ak-ˈti-nē-əm How to pronounce actinium (audio)
: a radioactive trivalent metallic element that resembles lanthanum in chemical properties and that is found especially in pitchblende see Chemical Elements Table

Example Sentences

Recent Examples on the Web Other theorists have predicted that hydrides such as calcium hydride or actinium hydride should superconduct at close to room temperature—and at a pressure considerably less than that needed for CSH. Robert F. Service, Science | AAAS, 26 Aug. 2021

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'actinium.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

Word History

Etymology

borrowed from French, from Greek aktīn-, aktís "ray, beam" + -ium -ium; so called from its radioactivity — more at actin-

First Known Use

1900, in the meaning defined above

Time Traveler
The first known use of actinium was in 1900

Dictionary Entries Near actinium

Cite this Entry

“Actinium.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/actinium. Accessed 27 Nov. 2022.

Kids Definition

actinium

noun

ac·​tin·​i·​um ak-ˈtin-ē-əm How to pronounce actinium (audio)
: a radioactive metallic element found especially in pitchblende see element

Medical Definition

actinium

noun

ac·​tin·​i·​um ak-ˈtin-ē-əm How to pronounce actinium (audio)
: a radioactive trivalent metallic element that resembles lanthanum in chemical properties and that is found especially in pitchblende
symbol Ac
see Chemical Elements Table

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