An Etymological Dictionary of the German Language/Annotated/Schweiß
Schweiß, masculine, ‘sweat, perspiration,’ from the equivalent Middle High German and Old High German sweiȥ, masculine; Middle High German also ‘blood,’ a meaning still current among sportsmen (so too schweißen, ‘to bleed’); Old Saxon swêt, ‘sweat,’ Anglo-Saxon swât, ‘sweat, blood,’ English sweat, Dutch zweet. For the Teutonic root swī̆t, swait, Aryan swoid, swī̆d, see under schwißen; compare Sanscrit svẽda-s, masculine, Latin sudor (from *svoidos), ‘sweat.’ To this is allied schweißen, verb, ‘to begin to melt, weld,’ from Middle High German sweiȥen, sweitzen, ‘to weld, Old High German sweiȥen, ‘to roast, broil.’