An Etymological Dictionary of the German Language/Annotated/Schwiele

Schwiele, feminine, ‘hard skin, weal,’ from the equivalent Middle High German swil, masculine and neuter, Old High German swilo, masculine, swil, neuter; Teutonic *swiliz, pre-Teutonic *swelos, neuter, is to be assumed; allied to the root swel in schwellen, Schwulst. Schwiele, literally ‘swelling.’