mad / mad/ • adj. (mad·der , mad·dest ) mentally ill; insane: he felt as if he were going mad. ∎  (of a person, conduct, or an idea) extremely foolish or ill-advised: they were all mad to go believing such a cock-and-bull story. ∎  in a frenzied mental or physical state: she pictured loved ones mad with anxiety about her it was a mad dash to get ready. ∎ inf. enthusiastic about someone or something: I wasn't mad about mountain bikes | [in comb.] a sports-mad nation. ∎ inf. very angry: they were mad at each other. ∎  (of a dog) rabid. ∎ Brit., inf. very exciting.• v. (mad·ded / madəd/ , mad·ding ) [tr.] archaic make mad or insane.PHRASES: like mad inf. with great intensity, energy, or enthusiasm: I ran like mad. (as) mad as a hatter inf. completely crazy.

mad don't get mad, get even there is more satisfaction in requiting a wrong than resenting it. Proverbial saying, late 20th century (compare the earlier revenge is a dish that can be eaten cold).
mad as a hatter completely insane. Hat-makers sometimes suffered from mercury poisoning as a result of the use of mercurous nitrate in the manufacture of felt hats, and the idea was personified in one of the two eccentric hosts (the Mad Hatter) at the ‘mad tea party’ in Lewis Carroll's Alice's Adventures in Wonderland (1865).
mad as a March hare completely insane; the allusion here is to the running and leaping of hares in the breeding season, and again was reinforced by the character created by Lewis Carroll in Alice's Adventures in Wonderland (1865).

See also whom the gods would destroy, they first make mad.

mad out of one's mind, foolish, (now) insanely foolish; wildly excited, furious. XIII (mad, med). Aphetic of ME. † amad, repr. OE. ǵemǣd(d), ġemǣded, pp. of *ġemǣdan render insane, f. ġemād insane = OS. gimēd foolish, OHG. gameit, kimeit foolish, vain, boastful. Goth. gamaips crippled:- Gmc. *ʒamaiōaz, f. *ʒa- y- + *maiða- :- IE. *moitó-, pp. formation on *moi- *mei- change (cf. L. mūtāre); cf. Goth. maidjan adulterate, inmaideins exchange.
Hence madden XVIII (-EN5); superseded mad vb. (XIV) in gen. use.

MAD (mæd) magnetic anomaly detection
• maintenance, assembly, and disassembly
• Psychiatry major affective disorder
• Commerce mean absolute deviation
• Military mutual assured destruction

MAD • abbr. mutual assured destruction.