iodine (n.)
1814, formed by English chemist Sir Humphrey Davy (1778-1829) from French iode "iodine," coined 1812 by French chemist Joseph Louis Gay-Lussac from Greek ioeides "violet-colored," from ion "the violet; dark blue flower," + eidos "appearance" (see -oid). Davy added the chemical suffix -ine (2) to make it analogous with chlorine and fluorine. So called from the color of the vapor given off when the crystals are heated.