An Etymological Dictionary of the German Language/Annotated/Wasen
Wasen, masculine, ‘sod, turf, grass,’ from Middle High German wase, Old High German waso, masculine, ‘sward, damp soil or mound’; also Old High German wasal, neuter, ‘damp mound.’ The word is identical with Rasen, just as sprechen with English to speak; compare Anglo-Saxon węččęan, wręččęan, ‘to awake,’ and Anglo-Saxon wrîxl with Wechsel. Hence there existed Aryan roots with and without r; we must therefore regard wraso, waso, as the Teutonic base; for the area of diffusion see Rasen. From Old High German is derived French gazon, ‘sward.’