1.  iodine(n = noun.substance) atomic number 53, i, iodin - a nonmetallic element belonging to the halogens; used especially in medicine and photography and in dyes; occurs naturally only in combination in small quantities (as in sea water or rocks);
is a kind of chemical element, element, halogen
has particulars: iodine-131, iodine-125
Derived forms verb iodinate₁, verb iodise₁, verb iodize₁

2.  iodine(n = noun.artifact) tincture of iodine - a tincture consisting of a solution of iodine in ethyl alcohol; applied topically to wounds as an antiseptic;
is a kind of antiseptic, tincture

   A nonmetallic element, of the halogen group of atomic number 53, occurring always in combination, as in the iodides. When isolated it is in the form of dark gray metallic scales, resembling plumbago, soft but brittle, and emitting a chlorinelike odor. Symbol I. Atomic weight 126.90. If heated, iodine volatilizes in beautiful violet vapors. [1913 Webster]
" Iodine was formerly obtained from the ashes of seaweed (kelp or varec), but is now also extracted from certain natural brines. In the free state, iodine, even in very minute quantities, colors starch blue. Iodine and its compounds are largely used in medicine (as in liniments, antisyphilitics, etc.), in photography, in the preparation of aniline dyes, and as an indicator in titration." [1913 Webster]

iodine, n.
1 Chem. a non-metallic element of the halogen group, forming black crystals and a violet vapour, used in medicine and photography, and important as an essential element for living organisms.

Usage:
Symb.: I.
2 a solution of this in alcohol used as a mild antiseptic.

Etymology:
F iode f. Gk iodes violet-like f. ion violet + -INE(4)

radioactive iodine excretion test, radioactive iodine test, radioactive iodine uptake test, tincture of iodine