lipid (n.)

word-forming element meaning "fat" (n.), from Greek lipos "fat" (n.), from PIE root *leip- "to stick, adhere," also used to form words for "fat."

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]