An Etymological Dictionary of the German Language/dauern
dauern (1.), vb., ‘to last, endure,’ from the equiv. MidHG. dûren, tûren, from Lat. dûrare (Fr. durer). Dauer, f., is simply a ModHG. form from dauern. E. to dure (endure) comes from Fr. durer.
dauern (2.), bedauern, vb., ‘to cause pity, sorrow, regret’; the initial d indicates that the vb. was borrowed from MidG. and LG., for the MidHG. 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, MidHG. tiure; for the change from û to iu comp. traurig with AS. dreórig, E. dreary. It is remarkable that the verb, which, judging by its gradation, must be very old, is utterly wanting in the older dialects.