iodine: [19] Íon was the Greek word for ‘violet’ (indeed it is related to English violet). From it was derived the adjective iódēs ‘violetcoloured’, which was taken by the chemist Joseph Louis Gay-Lussac as the basis of iode, the French term for ‘iodine’ (iodine gives off a purple vapour when heated). The British chemist Sir Humphry Davy adopted it into English, adding the suffix -ine to produce iodine. => violet[iodine etymology, iodine origin, 英语词源]
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.