From Middle High German rîter, rîtære, from Old High German rîtari. Not of Proto-Germanic age, but an OHG formation from the verb rītan "to ride" (Anglo-Saxon rîdere and Old Icelandic ríðari are loans from OHG).
Low German has riddere, with short vowel and geminate. Middle High German forms seem to have varied between long and short vowel, riter vs. rîter respectively, the latter giving rise to the separate word Ritter (“knight”). Lachmann (1827) noted that Middle High German poetry avoided use of the word in rhyming position, indicating that the two forms were used interchangeably.[1]
Reiter m (strong, genitive Reiters, plural Reiter, feminine Reiterin)
From Middle High German rītere, from Old High German rîtera, attested as glossing cribrum, from Proto-West Germanic *hrīdrā (“sieve”). Cognate with Old English hridder (English riddle (“sieve”)); also Latin cribrum, Ancient Greek κρίμνον (krímnon) (κρίνω (krínō)). Early New High German forms reyter, raiter, reuter.
Reiter f (genitive Reiter, plural Reiter)
Reiter m or f (proper noun, surname, masculine genitive Reiters or (with an article) Reiter, feminine genitive Reiter, plural Reiters or Reiter)