noun, often attributive
io·​dine | \ˈī-ə-ˌdīn, -dᵊn, -ˌdēn\

Definition of iodine 

1 : a nonmetallic halogen element obtained usually as heavy shining blackish-gray crystals and used especially in medicine, photography, and analysis — see Chemical Elements Table

2 : a tincture of iodine used especially as a topical antiseptic

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Did You Know?

Iodine is a nonmetallic chemical element and the heaviest nonradioactive halogen. It is a very nearly black crystalline solid that can turn to a deep violet, irritating vapor. In nature it is never found uncombined, and occurs mostly in brines and seaweeds. Dietary iodine is essential for thyroid gland function, so table salt usually has potassium iodide added to prevent iodine deficiency. Elemental iodine is used in medicine, in synthesizing some organic chemicals, in manufacturing dyes, in analytical chemistry, and in photography. The radioactive isotope I-131, with an eight-day half-life, is very useful in medicine and other applications.

Examples of iodine in a Sentence

Recent Examples on the Web

The thyroid gland needs iodine to produce hormones that regulate the body’s energy and metabolism. Erika Butler, The Aegis, "Harford residents near Peach Bottom atomic plant need potassium iodide on hand," 23 May 2018 For example, cesium and iodine are volatile, and these are far more likely to be released into the atmosphere than elements like plutonium. Andrew Karam, Popular Mechanics, "Five Years Later, Cutting Through the Fukushima Myths," 11 Mar. 2016 Radioactive iodine therapy to treat hypothyroidism’s foil, hyperthyroidism (an overactive thyroid), can be a cause, too. Carolyn L. Todd, SELF, "Are Hashimoto’s Disease and Hypothyroidism the Same Thing?," 14 May 2018 Spending time in a room heavily infused with the aroma of smoked grains cooking made my sweater smell like iodine and ashes for days. Liza Weisstuch, New York Times, "The Whisky Chronicles," 23 Apr. 2018 In Hawaii and other parts of the United States, there has been, for example, a spike in sales of potassium iodide, a drug that can block the thyroid gland from absorbing radioactive iodine released in a nuclear attack. Clyde Haberman, New York Times, "‘This Is Not a Drill’: The Growing Threat of Nuclear Annihilation," 13 May 2018 Russia's Energia Rocket and Space Corporation (aka S.P. Korolev Rocket and Space Corporation Energia) is developing a new electric propulsion rocket engine operating on iodine, TASS reports. Eric Berger, Ars Technica, "Rocket Report: Small sat market surging, Proton dying, Falcon Heavy certified," 29 June 2018 Also, American food is highly fortified -- with vitamin D in milk, iodine in salt, B vitamins in flour, even calcium in some brands of orange juice. Liz Szabo, CNN, "Enthusiasm over vitamins often outpaces evidence, experts say," 13 Apr. 2018 Fish is high in many important nutrients, including high quality protein, iodine and various vitamins and minerals. Orthocincy,, "Benefits of eating fish," 19 June 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'iodine.' 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 iodine

1814, in the meaning defined at sense 1

History and Etymology for iodine

French iode "iodine" (borrowed from Greek ioeidḗs "violet-colored," from íon "the color violet"—going back to *wion, akin to the source of Latin viola "the violet flower"— + -o-eidēs -oid entry 2) + -ine entry 2 (after chlorine, fluorine) — more at violet

Note: The French word iode was apparently introduced by the chemists Bernard Courtois (1777-1838) and Joseph Louis Gay-Lussac (1778-1850); cf. B. Courtois, "Découverte d'une substance nouvelle dans le Vareck," Annales de chimie, tome 88 (1813), p. 305: "La substance nouvelle, que depuis on a nommé iode à cause de la belle couleur violette de sa vapeur, a bien tout l'aspect d'un métal." ("The new substance, which since has been named iode because of the beautiful violet color of its vapor, has all the appearance of a metal.") Note that a borrowing from Greek ioeidḗs should properly have yielded ioïde in French rather than iode; the direct source of the latter may have been iṓdēs "rust-colored," a derivative of íos "rust, verdigris," taken erroneously to be a derivative of íon "the color violet."

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Statistics for iodine

Last Updated

11 Nov 2018

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Time Traveler for iodine

The first known use of iodine was in 1814

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More Definitions for iodine



English Language Learners Definition of iodine

: a chemical element that is used especially in medicine and photography


io·​dine | \ˈī-ə-ˌdīn, -dᵊn\

Kids Definition of iodine

1 : a chemical element found in seawater and seaweeds and used especially in medicine and photography

2 : a solution of iodine in alcohol used to kill germs


noun, often attributive
io·​dine | \ˈī-ə-ˌdīn, -əd-ᵊn, -ə-ˌdēn \

Medical Definition of iodine 

1 : a nonmetallic halogen element obtained usually as heavy shining blackish gray crystals and used especially in medicine (as in antisepsis and in the treatment of goiter and cretinism) and in photography and chemical analysis symbol I — see Chemical Elements Table

2 : a tincture of iodine used especially as a topical antiseptic

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Comments on iodine

What made you want to look up iodine? Please tell us where you read or heard it (including the quote, if possible).


noxious or harmful

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