An Etymological Dictionary of the German Language/Annotated/reich
reich, adjective, ‘rich, copious, abounding,’ from Middle High German rîhhi, Old High German rîhhi, adjective, ‘mighty, rich, splendid’; corresponding to Old Saxon rîki, ‘mighty, powerful,’ Anglo-Saxon rîce, ‘mighty, powerful,’ English rich, Gothic reiks, ‘mighty, distinguished.’ From the German adjective the equivalent Romance cognates are derived; compare Italian ricco, French riche, ‘rich.’ The comon Teutonic adjective is a derivative of the root *rîk, ‘king,’ discussed under the preceding word, hence ‘mighty’ is the earlier meaning of the cognates; ‘royal’ (Latin régius) is the original sense.