An Etymological Dictionary of the German Language/rasch
rasch, adj., ‘impetuous, speedy, swift, rash,’ from MidHG. rasch, OHG. rasc, adj., ‘quick, prompt, skilful, powerful,’ of which the equiv. variants MidHG. and OHG. rosch, and MidHG. resch, risch, occur. Corresponding to E. rash, Du. rasch; OIc. rǫskr (Goth. *rasqs), ‘brave.’ The final dental of the root has disappeared before the suffix sqa, ska (*rasqa- for *rat-sqa); comp. OHG. rado, AS. rœde, ‘quick.’ Comp. also OIc. horskr, AS. horsc, ‘quick, clever,’ with AS. hrœdlîc, ‘quick.’ The Teut. root raþ, Aryan rot (roth), in OHG. rado, ‘quick,’ may have meant ‘to hasten’; it appears also in ModHG. Rad.