From Middle Dutch ruuch, ru, rou, from Old Dutch *rūh, *rū, from Proto-Germanic *rūhaz. 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 on other words with -ch in the uninflected form and -g- in inflected forms, similar to what happened to hoog.
|Tense \ Voice||Active||Passive|
|Present||a' ruigsinn/a' ruighinn/a' ruigheachd||--|