An Etymological Dictionary of the German Language/Stiefel
Stiefel, m., ‘boot,’ from the equiv. MidHG. stivel, stivâl (OHG. stivâl?), m.; the MidHG. variant stivâl points clearly to a loan-word from the equiv. Ital. stivále, m. (for v equiv. to MidHG. v, f, comp. Vers, Käfig), lit. ‘a light summer covering made of leather for the feet’ (from MidLat. œstivale, ‘pertaining to summer’). The word was borrowed in HG. (it does not occur in the other Teut. dialects), probably in the 12th cent.