köken: From Middle High German rūch, from Old High German rūh, from Proto-Germanic *rūhwaz. Though etymologically justified, the silent h was abolished in 1996 because rauh was the only word in which it was used after the diphthong -au-. Cognate with Dutch ruig and ruw, English rough (which see).
köken: From Middle Dutch ruuch, ru, rou, from Old Dutch *rūh, *rū, from Proto-Germanic *rūhaz, *rūhwaz. The original stem ended in -h-, which disappeared between vowels, giving *rū- in the inflected forms in Old Dutch. This then gave rise to an alternative uninflected form *rū, which developed into Middle Dutch ru, rou, modern Dutch ruw, rouw. The original uninflected form was back-formed to ruig based…