Iodine is a chemical element (symbol I). In a school lab you meet it as a dark, almost violet-black solid; if you warm it, the vapour is a striking purple — and that colour is why it got its name. Families also know it as the stuff put on cuts to kill germs. Though actually, what you paint on a wound is usually not the pure element. Learner books sometimes call it “dark blue”; the colours people remember are purple vapour and a brown stain on skin. In a Taiwan pharmacy the old brown liquid is 碘酒; the milder reddish antiseptic many people ask for is 優碘, an iodine mix, not the stinging brown liquid alone. It is a science word, but a household one too because of first aid.