iodine

American  

[ahy-uh-dahyn, -din, ahy-uh-deen] / ˈaɪ əˌdaɪn, -dɪn, ˈaɪ əˌdin /

Sometimes iodin

noun

Chemistry.

1. a nonmetallic halogen element occurring at ordinary temperatures as a grayish-black crystalline solid that sublimes to a dense violet vapor when heated: used in medicine as an antiseptic. I; 126.904; 53; (solid) 4.93 at 20°C.

---

iodine British  

/ ˈaɪəˌdiːn /

noun

1. a bluish-black element of the halogen group that sublimates into a violet irritating gas. Its compounds are used in medicine and photography and in dyes. The radioisotope iodine-131 ( radioiodine ), with a half-life of 8 days, is used in the diagnosis and treatment of thyroid disease. Symbol: I; atomic no: 53; atomic wt: 126.90447; valency: 1, 3, 5, or 7; relative density: 4.93; melting pt: 113.5°C; boiling pt: 184.35°C

---

iodine Scientific  

/ ī′ə-dīn′ /

1. A shiny, grayish-black element of the halogen group. It is corrosive and poisonous and occurs in very small amounts in nature except for seaweed, in which it is abundant. Iodine compounds are used in medicine, antiseptics, and dyes. Atomic number 53; atomic weight 126.9045; melting point 113.5°C; boiling point 184.35°C; specific gravity (solid, at 20°C) 4.93; valence 1, 3, 5, 7.

2. See Periodic Table

---

Etymology

Origin of iodine

First recorded in 1814; from French iode + -ine ² ( def. 2 ); introduced by H. Davy. Ultimately from Greek īṓdēs, originally “rust-colored”, but by folk etymology taken as í(on) “violet” + -ōdēs noun suffix; see -ode ¹ ( def. )

Compare meaning

How does iodine compare to similar and commonly confused words? Explore the most common comparisons:

• iodide vs. iodine
• Betadine vs. iodine
• povidone-iodine vs. iodine

Example Sentences

A short walk along an irrigation canal leads to a weathered observation deck rising two stories above a patchwork of saturated flats where saltgrass, iodine bush and cattail take root.

From Los Angeles Times • Apr. 7, 2026

Full-fat cheese contains several nutrients relevant to brain health, including fat-soluble vitamins A, D and K2, as well as vitamin B12, folate, iodine, zinc and selenium.

From Science Daily • Feb. 4, 2026

Their checklist also includes iodine tablets, as well as easy-to-cook food, pet food and a backup power supply.

From BBC • Nov. 17, 2024

Many seaweeds contain phenolic and flavonoid compounds, which are important antioxidants, as well as omega-3 fatty acids, amino acids, fibre, vitamins A, C and E – and minerals such as copper, zinc and iodine.

From Salon • Aug. 5, 2024

She thinks my eyes look better though you can’t tell with all that brown stuff, which looks and smells like iodine and if it’s anything like iodine it must burn.

From "Angela's Ashes: A Memoir" by Frank McCourt