An Etymological Dictionary of the German Language/Annotated/frank
frank, adjective, ‘free, independent,’ first occurs in Modern High German, from French franc (Italian, Spanish, and Portuguese franco), which was again derived from the Teutonic tribal name Franken, Old High German Franchun, and may have been applied generally to any freeman. The term Franken is properly a derivative of a lost Old High German *francho, ‘javelin,’ preserved in Anglo-Saxon franca and Old Icelandic frakke; the Saxons (Sachsen) are similarly named after a weapon — Old High German Sahsun, from sahs, ‘sword’ (see Messer).