often attributive
: 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
: 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 Vinegar is sometimes used to disinfect wounds, with no iodine left. Abu Bakr Bashir, New York Times, 6 Nov. 2023 Excessive iodine intake can lead to thyroid dysfunction, including hyperthyroidism or hypothyroidism. Jake Parks, Discover Magazine, 23 Oct. 2023 The letter stemmed from a public forum at Pathway Church in Redding in which those physicians promoted the use of home remedies — including vitamins and iodine nasal sprays — to prevent and treat COVID-19. Hailey Branson-Potts, Los Angeles Times, 19 Oct. 2023 El Moussa then took a few weeks to process his diagnosis but eventually scheduled his surgeries and radioactive iodine therapy in order to successfully beat the cancers. Claudia Harmata, Peoplemag, 2 Aug. 2023 High in vitamin D as well as iodine and selenium which support healthy thyroid function, these fish are also rich in anti-inflammatory omega-3s. Georgia Day, Vogue, 6 Sep. 2023 In the new study, vegetarians consumed less dietary protein, iron, iodine, niacin, selenium, vitamin B12, and vitamin D than other diet groups. Lauren Manaker Ms, Rdn, Health, 24 Aug. 2023 These supplements often contain higher amounts of iron, calcium, vitamin D, omega-3 fatty acids, iodine, and vitamin B12 to compensate for potential deficiencies. Amber Smith, Discover Magazine, 13 Aug. 2023 For example, the Japanese diet, high in fish and seaweed, provides omega-3 fatty acids and iodine, while Mediterranean and Caribbean diets offer an abundance of fruits, vegetables, whole grains, and healthy fats. Dezi Abeyta, Men's Health, 26 July 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'iodine.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


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."

First Known Use

1814, in the meaning defined at sense 1

Time Traveler
The first known use of iodine was in 1814

Dictionary Entries Near iodine

Cite this Entry

“Iodine.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/iodine. Accessed 1 Dec. 2023.

Kids Definition


io·​dine ˈī-ə-ˌdīn How to pronounce iodine (audio)
variants also iodin
: a nonmetallic element that is obtained usually as heavy shining blackish gray crystals and is used especially in medicine and photography see element
: a solution of iodine in alcohol used to kill germs

Medical Definition


often attributive
: 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
: a tincture of iodine used especially as a topical antiseptic

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