iodine

UK: /ˈaɪədiːn/

US: /ˈaɪəˌdaɪn, -dɪn; in Chemistry also -ˌdin/

US: (ī′ə dīn′, -din; in Chem. also ī′ə dēn′)

WordReference Random House Learner's Dictionary of American English © 2026

i•o•dine /ˈaɪəˌdaɪn, -dɪn; in Chemistry also -ˌdin/,  also i•o•din /ˈaɪədɪn/   n. [uncountable]

1. Chemistry, Drugs a dense, violet-colored substance used as an antiseptic on wounds, as a nutritional supplement, and in photography.

WordReference Random House Unabridged Dictionary of American English © 2026

i•o•dine  (ī′ə dīn′, -din; in Chem. also ī′ə dēn′), n. [Chem.]

1. Chemistry, Drugs 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. Symbol: I;
   at. wt.: 126.904;
   at. no.: 53;
   sp. gr.: (solid) 4.93 at 20°C.

Also, i•o•din  (ī′ə din). 

• Greek īó̄dēs, origin, originally rust-colored, but by folk etymology, etymological taken as í(on) violet + -ōdēs -ode¹) + -ine²; introduced by H. Davy
• French iode (
• 1814

Collins Concise English Dictionary © HarperCollins Publishers::

iodine / 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

Etymology: 19th Century: from French iode, from Greek iōdēs rust-coloured, but taken to mean violet-coloured, through a mistaken derivation from ion violet