An Etymological Dictionary of the German Language/mahnen
mahnen, vb., ‘to warn, admonish,’ from MidHG. manen, OHG. manôn, manên, ‘to remind, warn, challenge’; corresponding to OSax. manôn, AS. manian, ‘to. warn’; a derivative of the Aryan root mon, men, widely diffused in OTeut., to which are allied the Goth. pret. pres. munan, ‘to be of opinion,’ Lat. memini, reminiscor, men-s (men-te-m), Gr. μένος, μιμνήσκω, and the Sans. root man, ‘to think’ (see Mann, meinen, and Minne). To OHG. manên (with the variant monên), Lat. monêre, ‘to warn,’ with ŏ equiv. to Teut. a (as in Lat. molere, Goth. and OHG. malan), which is likewise formed from the root men, is most closely allied in sound and meaning.