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

Examples of actinium in a Sentence

Recent Examples on the Web Those protons smashing and staying put creates the right kind of actinium through a process called spallation. Sarah Scoles, Scientific American, 13 Feb. 2024 For years, scientists have produced this species of actinium by waiting for thorium (element 90, with one extra proton than actinium) to decay. Sarah Scoles, Scientific American, 13 Feb. 2024 The lanthanide and actinide series — those two rows floating by themselves, named after their first members, lanthanum and actinium — are isolated like that as a concession to limited space. Bill Andrews, Discover Magazine, 26 June 2019 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 examples are programmatically compiled from various online sources to illustrate current usage of the word 'actinium.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

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 May. 2024.

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

More from Merriam-Webster on actinium

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!