There is a folk story that it comes from “De-Rabanan”.
I believe more likely it is related to the the English word “devine”, meaning it is of Latin/Old French origin (remember that Asheknazim arrived in German-speaking areas where we invented Yiddish after moving through areas that spoke Latin or other Romance languages, which is where Yiddish picked up some words of Latin origin). Note that “Bentsch” (related to English “benediction”) is also a Yiddish word for a religious term derived from a Latin route.