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 on other words with -ch in the uninflected form and -g- in inflected forms, similar to what happened to hoog.
ruig (comparative ruiger, superlative ruigst)
| Declension of ruig | ||||
|---|---|---|---|---|
| uninflected | ruig | |||
| inflected | ruige | |||
| comparative | ruiger | |||
| positive | comparative | superlative | ||
| predicative/adverbial | ruig | ruiger | het ruigst het ruigste | |
| indefinite | m./f. sing. | ruige | ruigere | ruigste |
| n. sing. | ruig | ruiger | ruigste | |
| plural | ruige | ruigere | ruigste | |
| definite | ruige | ruigere | ruigste | |
| partitive | ruigs | ruigers | — | |
ruig (past ràinig, future ruigidh, verbal noun ruigsinn or ruighinn or ruigheachd, past participle ruigte)