sulfide (n.)

also sulphur, c. 1300, from Anglo-French sulfere, Old French soufre "sulfur, fire and brimstone, hellfire" (13c.), later also sulphur, from Late Latin sulfur, from Latin sulphur, probably from a root meaning "to burn." Ousted native brimstone and cognate Old English swefl, German schwefel, Swedish swafel, Dutch zwavel. The spelling with -ph- is standard in Britain, but its suggestion of a Greek origin is misleading.

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]