An Etymological Dictionary of the German Language/Grund
Grund, m., ‘ground, earth, basis, rudiment, reason,’ from the equiv. MidHG. grunt(d), OHG. grunt, m.; corresponding to Du. grond, AS. grund, E. ground, OIc. grund, ‘meadow land,’ grunnr (from grun-þus), ‘bottom of the sea;’ Goth. grundu-waddjus, ‘foundation wall.’ Goth. grundu, from pre-Teut. ghrentu- (with t on account of OIc. grunnr), cannot have originated in the Teut. root grind (pre-Teut. ghrendh) mentioned under Grand. No cognates are found in the non-Teut. languages.