An Etymological Dictionary of the German Language/Annotated/Reiter
Reiter, feminine, ‘coarse sieve, riddle,’ from Middle High German rîter, Old High German rîtara, feminine, ‘sieve,’ for earlier *hrîtara; corresponding to Anglo-Saxon hrîdder, feminine, ‘sieve’ whence English riddle. For the Teutonic root hrî in the sense of ‘to sift, winnow,’ see rein. The Old High German suffix tara, from pre-Teutonic thrâ (Gothic *hrei-dra, feminine), corresponds to -brum for -thrum in Latin cribrum (br from thr, as in ruber, ἐρυθρός), equivalent to Old Irish críathar, ‘sieve’; Aryan kreithro- may be assumed. Modern High German Räder, ‘sieve,’ is not connected with this word.