cui bono Look up cui bono at Dictionary.com
a Latin phrase from Cicero. It means "to whom for a benefit," or "who profits by it?" not "to what good purpose?" as is often erroneously claimed. 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-).