An Etymological Dictionary of the German Language/Annotated/Stiefel
Stiefel, masculine, ‘boot,’ from the equivalent Middle High German stivel, stivâl (Old High German stivâl?), masculine; the Middle High German variant stivâl points clearly to a loan-word from the equivalent Italian stivále, masculine (for v equivalent to Middle High German v, f, compare Vers, Käfig), literally ‘a light summer covering made of leather for the feet’ (from Middle Latin œstivale, ‘pertaining to summer’). The word was borrowed in High German (it does not occur in the other Teutonic dialects), probably in the 12th century.