mad

\ \ [13] The underlying etymological meaning of mad is ‘changed’. It goes back ultimately to Indo-European *moitó-, a past participial form based on *moi-, *mei-, ‘change’ (source also of Latin mūtāre ‘change’, from which English gets mutate). Prehistoric Germanic inherited it, adding the collective prefix *ga- to form *gamaithaz, which passed into Old English as gemād ‘insane’. From this was derived the verb gemǣdan ‘madden’, whose past participle gemǣded eventually became a new adjective gemǣdd. By the Middle English period this had become amadd, and the reduced prefix aeventually disappeared, leaving mad.

\ \ Cf.⇒ MUTATE