iodin n 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) Usage(s) TREATMENT: radioactive iodine, phosphorus and gold are effective in half a dozen diseases, though in no more. The established theory is that goiter is due to lack of iodine in food drink. In some places iodine is found in natural salt deposits as an "impurity. Synonym(s) iodine I atomic number 53