An Etymological Dictionary of the German Language/Walnuß
Walnuß, f., ‘walnut,’ ModHG. only, from the equiv. Du. walnoot; comp. AS. wealhhnutu, E. walnut, OIc. walhnot; it signifies ‘French or Italian nut.’ The first component is walh-, a term orig. applied by the Teutons to the Kelts (at first to the Volcae), but later to the Romance tribes of France and Italy. See welsch.