Etymology
1. O.E.
gemædde (pl.) "out of one's mind" (usually implying also violent excitement), also "foolish," earlier
gemæded "rendered insane," pp. of a lost verb
*gemædan "make mad," from
gemad "mad," from P.Gmc.
*gamaithaz "changed (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
*ge- + 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"). Emerged in M.E. to replace the more usual O.E. word,
wod. Sense of "beside oneself with excitement or enthusiasm" is from c.1330. 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.
Madcap (n. and adj.) is from 1588;
madhouse is from 1687. Phrase
mad as a March hare is attested from 1529, 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.
2. From Middle English madden, from the adjective; compare Old English ġemǣdan. See: Middle English '
madden'.