a chemical element. Iodine is a substance found in seawater. A liquid containing iodine is sometimes used as an antiseptic (= a substance used on wounds to prevent infection). Topics Physics and chemistryc2碘 Word Originearly 19th cent.: from French iode (from Greek iōdēs ‘violet-coloured’, from ion ‘violet’ + -eidēs ‘like’) + -ine.