köken: From north-eastern Middle High German rase, probably from Middle Low German wrāse (“sod, turf”), though the two could also be cognate forms. Further origin presumably a variant of Middle Low German wāse, from Old Saxon waso, from Proto-West Germanic *wasō (“moisture, slime, muck”) which has been inherited as German Wasen. The intermitting r might be due to influence from dialectal forms of Brodem…
köken: From vireō (“to be green, verdant”) + -tum (suffix forming nouns for stands of vegetation). The -c- would be inserted by analogy to forms like frutectum (“thicket, bush”), cārectum (“reed bed”) that are derived from noun stems ending in /k/.