madyoudaoicibaDictYouDict[mad 词源字典]
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.
=> mutate[mad etymology, mad origin, 英语词源]
mad (adj.)youdaoicibaDictYouDict
late 13c., from Old English gemædde (plural) "out of one's mind" (usually implying also violent excitement), also "foolish, extremely stupid," earlier gemæded "rendered insane," past participle of a lost verb *gemædan "to make insane or foolish," from Proto-Germanic *ga-maid-jan, demonstrative form of *ga-maid-az "changed (for the worse), abnormal" (cognates: Old Saxon gimed "foolish," Old High German gimeit "foolish, vain, boastful," Gothic gamaiþs "crippled, wounded," Old Norse meiða "to hurt, maim"), from intensive prefix *ga- + PIE *moito-, past participle of root *mei- (1) "to change" (cognates: Latin mutare "to change," mutuus "done in exchange," migrare "to change one's place of residence;" see mutable).

Emerged in Middle English to replace the more usual Old English word, wod (see wood (adj.)). Sense of "beside oneself with excitement or enthusiasm" is from early 14c. Meaning "beside oneself with anger" is attested from early 14c., but deplored by Rev. John Witherspoon (1781) as an Americanism. It now competes in American English with angry for this sense. Of animals, "affected with rabies," from late 13c. Phrase mad as a March hare is attested from 1520s, via notion of breeding season; mad as a hatter is from 1829 as "demented," 1837 as "enraged," according to a modern theory supposedly from erratic behavior caused by prolonged exposure to poison mercuric nitrate, used in making felt hats. For mad as a wet hen see hen. Mad money is attested from 1922; mad scientist is from 1891.
mad (adv.)youdaoicibaDictYouDict
late 14c., from mad (adj.).