An Etymological Dictionary of the German Language/sieben

by Friedrich Kluge

sieben, num. ‘seven,’ from the equiv. MidHG. siben, OHG. sibun; corresponding to Goth. sibun, AS. seofon, E. seven, Du. zeven, OSax. siƀun, ‘seven’; orig. septn. Like all units, a common Aryan word; comp. Sans. saptan, Gr. ἑπτά, Lat. septem, OSlov. sedmĭ, OIr. secht, ‘seven.’ The t of the Aryan prim. form septn- disappears in primit. Teut. between p and n.