An Etymological Dictionary of the German Language/Annotated/dauern
dauern (1.), verb, ‘to last, endure,’ from the equivalent Middle High German dûren, tûren, from Latin dûrare (French durer). Dauer, feminine, is simply a Modern High German form from dauern. English to dure (endure) comes from French durer.
dauern (2.), bedauern, verb, ‘to cause pity, sorrow, regret’; the initial d indicates that the verb was borrowed from Middle German and Low German, for the Middle High German form was tûren; mich tûret ein ding or eines dinges, ‘that appears to me to be (too) expensive, dear’; tûren is related by gradation to teuer, Middle High German tiure; for the change from û to iu compare traurig with Anglo-Saxon dreórig, English dreary. It is remarkable that the verb, which, judging by its gradation, must be very old, is utterly wanting in the older dialects.