noun, often attributive
io·​dine | \ ˈī-ə-ˌdīn How to pronounce iodine (audio) , -dᵊn, -ˌdēn \

Definition of iodine

1 : a nonmetallic halogen element that is an essential nutrient in the human diet and is used especially in medicine, photography, and analytical chemistry — see Chemical Elements Table
2 : a tincture of iodine used especially as a topical antiseptic

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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 These include calcium, magnesium, vitamin E, vitamin D, several B vitamins, vitamin A, vitamin K, potassium, iodine, selenium, borate, zinc, manganese, molybdenum, beta-carotene, and iron. Allure, 25 Apr. 2022 Radioactive iodine ingested from radioactive fallout is concentrated in the thyroid gland, putting a person at risk from thyroid cancer. Dr. Keith Roach, oregonlive, 15 Feb. 2022 Medical items such as gauze, bandages, Advil, disinfectants, iodine, eyeglasses and diabetic syringes began to pill up. Teresa Moss, Arkansas Online, 11 Apr. 2022 During the cold winter months in 2017, the researchers flew aircraft to inject silver iodine, the seeding chemical used, into clouds over the Payette Basin in Idaho, while simultaneously using radars and models to measure its impact on snowfall. Jennifer Gray And Rachel Ramirez, CNN, 14 Mar. 2022 Other vital nutrients in fish include iron, iodine, selenium, zinc and vitamin B12. Bethany Thayer, Detroit Free Press, 19 Mar. 2022 Radioactive iodine still helps for high risk thyroid cancer, where the malignancy has already spread throughout the body. Angus Chen, STAT, 10 Mar. 2022 Taking the pills preventatively, if radioactive iodine is not present, can cause harm to the body. Megan Cerullo, CBS News, 9 Mar. 2022 Moreover, iodine is not a silver bullet solution for protecting oneself in a fallout. Christiaan Hetzner, Fortune, 8 Mar. 2022 See More

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.

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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Last Updated

3 May 2022

Cite this Entry

“Iodine.” Dictionary, Merriam-Webster, Accessed 28 May. 2022.

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More Definitions for iodine


io·​dine | \ ˈī-ə-ˌdīn How to pronounce iodine (audio) , -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 How to pronounce iodine (audio) , -əd-ᵊn How to pronounce iodine (audio) , -ə-ˌdēn How to pronounce iodine (audio) \

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

More from Merriam-Webster on iodine

Nglish: Translation of iodine for Spanish Speakers

Britannica English: Translation of iodine for Arabic Speakers Encyclopedia article about iodine


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