a Latin phrase from Cicero. It means "to whom for a benefit," or "who profits by it?" not "to what good purpose? for what use or end?" as is sometimes said. From cui "to? for whom?," an old form preserved here in the dative form of the interrogative pronoun quis "who?" (from PIE root *kwo-, stem of relative and interrogative pronouns) + bono "good" (see bene-).
also etcetera, early 15c., from Latin et cetera, literally "and the others," from et "and" + neuter plural of ceterus "the other, other part, that which remains," from Proto-Italic *ke-etero‑, from *ke-, variant form of PIE root *ko-, the stem of demonstrative pronoun meaning "this" + *etero‑ "other (of two), again, a second time, again," a PIE adjective of comparison.
The common form of the abbreviation before 20c. was &c., but etc. now prevails.