An Etymological Dictionary of the German Language/Fist
Fist, m., ‘fart,’ from the equiv. MidHG. vist, m.; akin to the equiv. Du. veest, AS. fist. A common Aryan root pezd appears in Lat. pêdo for pezdo, as well as in Gr. βδέω, from *βσδέω, Lith. bezdù (bezděti), Hence Teut. fisti- is to be explained by Aryan pezd-i-. From the verbal noun fist a verbal root fī̆s, ‘pedere,’ was inferred in very early times. Comp. OIc. físa.