irid·​i·​um | \ i-ˈri-dē-əm How to pronounce iridium (audio) \

Definition of iridium

: a rare silver-white hard brittle very heavy metallic element — see Chemical Elements Table

Examples of iridium in a Sentence

Recent Examples on the Web In 1980, the father and son team of Luis and Walter Alvarez, digging into a roadcut outside the town of Gubbio, Italy, discovered a layer of rock enriched in the element iridium. Smithsonian Magazine, Smithsonian Magazine, "Fifty Things We’ve Learned About the Earth Since the First Earth Day," 22 Apr. 2020 In October 2019, a study was published that said a brief ice age period occurred roughly 12,800 years ago and was caused by an asteroid impact, after researchers found high levels of iridium and platinum in White Pond near Elgin, S.C. Fox News, "Giant asteroid apocalypse 13K years ago was witnessed by ancient humans, experts believe," 12 Mar. 2020 Rather than basing the kilogram off of an object—a platinum-iridium alloy cylinder about the size of a golf ball—the new definition uses a constant of nature to set the unit of mass. Jay Bennett, Smithsonian Magazine, "The Top Ten Scientific Discoveries of the Decade," 6 May 2012 Precious metals like platinum and iridium were needed to boost efficiency, making a cheaper catalyst crucial. David Grossman, Popular Mechanics, "Make Hydrogen Cheap Again," 24 Oct. 2019 The official object that defines the mass of a kilogram is a tiny, 139-year-old cylinder of platinum and iridium that resides in a triple-locked vault near Paris. Clara Moskowitz, Scientific American, "Redefining the Kilogram," 1 Nov. 2018 Their key piece of evidence is an oddly high amount of the metal iridium in what’s known as the Cretaceous-Paleogene, or K-Pg, layer—the geologic boundary zone that seems to cap any known rock layers containing dinosaur fossils. Victoria Jaggard, National Geographic, "Why did the dinosaurs go extinct?," 31 July 2019 Iridium-192 is a radioactive isotope of the chemical element iridium, according to the U.S. National Center for Biotechnology Information. Washington Post, "Prime minister resigns after Hague summons," 20 July 2019 Dubbed Le Grande K, or Big K, this lonely hunk of platinum and iridium has defined mass around the globe for more than a century—from bathroom scales to medical lab balances. Robert Rathe, National Geographic, "The kilogram is forever changed. Here's why that matters.," 20 May 2019

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

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First Known Use of iridium

1804, in the meaning defined above

History and Etymology for iridium

Greek īrid-, îris "rainbow, iridescent halo around the moon, a flame, etc., iris entry 1" + New Latin -ium -ium; from the colors produced by dissolving it in hydrochloric acid

Note: The word iridium was introduced by the English chemist Smithson Tennant (1761-1815) in Philosophical Transactions of the Royal Society, 1804, Part II, p. 414: "As it is necessary to give some name to bodies which have not been known before, and most convenient to indicate by it some characteristic property, I should incline to call this metal Iridium, from the striking variety of colours which it gives, while dissolving in marine acid." See also osmium.

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The first known use of iridium was in 1804

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Cite this Entry

“Iridium.” Dictionary, Merriam-Webster, Accessed 6 Aug. 2020.

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More Definitions for iridium


irid·​i·​um | \ i-ˈri-dē-əm How to pronounce iridium (audio) \

Kids Definition of iridium

: a hard brittle heavy metallic chemical element


irid·​i·​um | \ ir-ˈid-ē-əm How to pronounce iridium (audio) \

Medical Definition of iridium

: a silver-white hard brittle very heavy metallic element of the platinum group used especially in hardening platinum for alloys (as for surgical instruments) symbol Ir — see Chemical Elements Table

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More from Merriam-Webster on iridium

Rhyming Dictionary: Words that rhyme with iridium

Spanish Central: Translation of iridium

Nglish: Translation of iridium for Spanish Speakers Encyclopedia article about iridium

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