An Etymological Dictionary of the German Language/Annotated/empören

by Friedrich Kluge

empören, verb, ‘to excite, enrage, (reflexive) to revolt,’ from Middle High German enbœren, Old High German (occurs only once) anabôren, ‘to raise’; akin to Middle High German bôr, masculine, ‘defiance, revolt.’ The origin of the cognates is uncertain, because it is difficult to determine whether the r is primitive or whether it is by a later change based upon s (z); with ber, ‘upper space’ — see empor — there seems to be a connection by gradation of u to au; Modern High German böse (Old High German bôsi) is not allied.