An Etymological Dictionary of the German Language/Sohle
Sohle (1.), f., ModHG. only, formed like the equiv. E. sole, Swed. sola, from the Lat.-Rom. term solea, ‘flat fish’; comp. Fr. sole, Ital. soglia. Is the term Scholle (Du. schol) derived from the same source?
Sohle (2.), f., ‘sole (of the foot),’ from the equiv. MidHG. sol, sole, OHG. sola, f.; borrowed contemporaneously with Socke prior to the OHG. period from Lat. *sŏla (a variant of sŏlea), which is implied by Ital. suolo, Fr. sole, ‘sole.’ Lat. sŏlea, whence Ital. soglia, Fr. seuil, ‘threshold,’ is probably the source of Goth. sulja, ‘sole.’ The prim. kinship of OHG. sola with Lat. solea (Gr. ὑλιώ) is conceivable if Schwelle is allied.