(for the worse), abnormal" (cf. O.S. gimed "foolish," O.H.G. gimeit "foolish, vain, boastful," Goth. gamaiþs "crippled, wounded," O.N. meiða "to hurt, maim"), from intensive prefix *ga- + PIE *moito-, pp. of base *mei- "to change" (cf. L. mutare "to change," mutuus "done in exchange," migrare "to change one's place of residence;" see mutable
). Emerged in M.E. to replace the more usual O.E. 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 c.1300, but deplored by Rev. John Witherspoon (1781) as an Americanism, and now competes in Amer.Eng. with angry
for this sense. Of dogs, "affected with rabies," from 1800. Phrase mad as a March hare is attested from 1520s, via notion of breeding season; mad as a hatter (1857) is said to be from erratic behavior caused by prolonged exposure to poison mercuric nitrate, used in making felt hats. Mad as a wet hen is from 1823. Mad money is attested from 1922; mad scientist is from 1940.
O.E. mædere "plant used for making dyes," from PIE *modhro- "dye plant" (cf. O.N. maðra, O.H.G. matara "madder," Pol. modry, Czech modry "blue").