word-forming element used from mid-20c. to mean "of or having to do with petroleum products," from petroleum.
word-forming element meaning "having one only," from Latin uni-, combining form of unus "one" (from PIE root *oi-no- "one, unique").
word-forming element in biological compounds meaning "be lacking, having no," from Greek leipein "to leave, be lacking," from PIE root *leikw- "to leave."
word-forming element meaning "three, having three, once every three," from Latin tres (neuter tria) or Greek treis, trias "three" (see three).
before vowels quinqu-, word-forming element from classical Latin meaning "five, consisting of or having five," from Latin quinque "five" (by assimilation from PIE root *penkwe- "five").
scientific word-forming element meaning "smooth," from Greek leios "smooth, level, flat; plain, unembroidered; beardless." E.g. leiotrichy, in ethnology, of races, "condition of having straight, lank hair" (1924).
word-forming element meaning "four, having four, consisting of four," a variant of quadri- which was used in Latin especially before -p-, from an older form of the element which perhaps was influenced later by tri-.
word-forming element meaning "social, of society; social and," also "having to do with sociology," from combining form of Latin socius "companion, ally, associate, fellow, sharer," from PIE *sokw-yo-, suffixed form of root *sekw- (1) "to follow." Common in compounds since c. 1880.
in Latin, the form of com- "together, with" in compounds with stems beginning in vowels, h-, and gn-; see com-. Taken in English from 17c. as a living prefix meaning "together, mutually, in common," and used promiscuously with native words (co-worker) and Latin-derived words not beginning with vowels (codependent), including some already having it (co-conspirator).