noun

1. a nonmetallic chemical element, one of the halogens, consisting of grayish-black crystals that volatilize into a violet-colored vapor: used as an antiseptic, in the manufacture of dyes, in photography, etc.: symbol, I; at. no., 53: a radioactive isotope (iodine-131) is used esp. in the diagnosis and treatment of thyroid function, in internal radiation therapy, and as a tracer
2. tincture of iodine, used as an antiseptic

Etymology: Fr iode, iodine (< Gr iōdēs, violetlike < ion, a violet + eidos, form: see -oid) + -ine