An Etymological Dictionary of the German Language/Schwefel
Schwefel, m., ‘brimstone, sulphur,’ from the equiv. MidHG. swëvel, swëbel, OHG. swëval, swëbal, m.; the f of the ModHG. form can only be explained by the influence of LG., as is shown by the double forms in MidHG. and OHG. A common Teut. word; comp. Du. zwavel, AS. swefl, Swed. swafvel, Goth. swibls, ‘sulphur.’ Lat. sulpur (for *suplur?) is probably not allied. If the OTeut. swebloz, ‘sulphur,’ is a primit. loan-word, it may perhaps be connected with the old Aryan root swep, ‘to sleep’ (Sans. svápnas, Lat. somnus, Gr. ὕπνος, AS. swëfn); comp. AS. swębban, ‘to kill,’ OIc. svœ́fa, ‘to kill, lull to sleep’; Schwefel may then be lit. ‘stifling, killing, soporific stuff.’