iodide (n.)

non-metallic element, 1814, formed by English chemist Sir Humphry Davy from French iode "iodine," which was coined 1812 by French chemist Joseph Louis Gay-Lussac from Greek ioeides "violet-colored" (from ion "the violet; dark blue flower;" see violet) + 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.

word-forming element used in chemistry to coin names for simple compounds of one element with another element or radical; originally abstracted from oxide, which was the first so classified, in which the -ide is from acide "acid."

The suffix is really -dus (-do-), the -i- repr. the orig. or supplied stem-vowel ; it occurs without the vowel in absurdus, absurd, blandus, bland, crudus, raw (crude), etc. [Century Dictionary]