An Etymological Dictionary of the German Language/Tochter
Tochter, f., ‘daughter,’ from the equiv. MidHG. tohter, OHG. tohter, f.; a common Teut., and also a primit. Aryan term; comp. Goth. daúhtar, AS. dohtor, E. daughter, Du. dochter, OSax. dohtar, ‘daughter.’ The primit Aryan dhuktêr (dhugatêr), on which the Teut. cognates are based, is indicated also by Lith. duktě, OSlov. dŭšti; comp. further Gr. θυγάτηρ, Sans. duhitâr, Zend duγδar, ‘daughter.’ The Aryan word is usually considered to be a derivative of the Sans. root dugh, ‘to milk,’ regarding Tochter as equiv. to ‘milker.’ This assumption is, however, quite as dubious as the derivation of Vater, Mutter, and Bruder.