They share many common linguistic features. One of them is that "Oïl" (pronounced [wil], or [wi] as in modern French "oui"), was the ancestor of the word for "yes" that is used in all of the Oïl languages. "Oc" is the word used in territories to the south and so the Occitan language is also called "langue d'oc" (literal English translation: "language of yes").