iodine

noun

io·​dine ˈī-ə-ˌdīn  -dᵊn  -ˌdēn 

1

: a nonmetallic halogen element with atomic number 53 that is an essential nutrient in the human diet and is used especially in medicine, photography, and analytical chemistry

—often used before another noun

iodine deficiency

iodine levels

iodine supplements

see Chemical Elements Table

2

: a tincture of iodine used especially as a topical antiseptic

The formerly popular antiseptic known as iodine is a tincture—a solution of iodine in alcohol.

—Regina and Douglas Haggo

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

Research shows that herring are packed with vitamin E, vitamin D, and B12, as well as minerals like selenium, iodine, calcium, and iron.10 Herring is low in toxins like lead, cadmium, and mercury, making herring a nutritious and safe seafood option to add to your diet. —Jillian Kubala, Health, 8 July 2025

In simpler terms, the particles, which were invented by researchers at The Chinese University of Hong Kong, contain a mix of the elements bismuth, oxygen and iodine along with the addition of a single atom of copper. —New Atlas, 30 June 2025

Far more dangerous than U-235 are the elemental products given off when nuclear fuel goes through fission—especially iodine, strontium, and cesium. —Jeffrey Kluger, Time, 24 June 2025

There was an examining table set up, and, once Hugh had changed into a medical gown, we were visited by six staff members, starting with a nurse who inserted an I.V. into the back of his hand and cleaned out his nose with iodine. —David Sedaris, New Yorker, 23 June 2025

Word History

Etymology

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

Phrases Containing iodine

• quartz-iodine lamp

Rhymes for iodine

• affine
• airline
• align
• aline
• assign
• baseline
• beamline
• benign
• bloodline
• bovine
• byline
• canine

Kids Definition

iodine

noun

io·​dine ˈī-ə-ˌdīn 

-əd-ᵊn,

-ə-ˌdēn

variants also iodin

ˈī-əd-ᵊn

1

: a nonmetallic element that is obtained usually as heavy shining blackish gray crystals and is used especially in medicine and photography see element

2

: a solution of iodine in alcohol used to kill germs

Medical Definition

iodine

noun

io·​dine ˈī-ə-ˌdīn  -əd-ᵊn  -ə-ˌdēn 

1

: a nonmetallic halogen chemical element with atomic number 53 that is an essential nutrient in the human diet and is used especially in medicine (as in antisepsis and in the treatment of goiter and cretinism), photography, and analytical chemistry

—symbol I see Chemical Elements Table

2

: a tincture of iodine used especially as a topical antiseptic