—adj. 1. mentally disturbed; deranged; insane; demented.
2. enraged; greatly provoked or irritated; angry.
3. (of animals)
a. abnormally furious; ferocious: a mad bull. b. affected with rabies; rabid: a mad dog. 4. extremely foolish or unwise; imprudent; irrational: a mad scheme to invade France. 5. wildly excited or confused: frantic: mad haste. 6. overcome by desire, eagerness, enthusiasm, etc.; excessively or uncontrollably fond; infatuated: He's mad about the opera. 7. wildly gay or merry; enjoyably hilarious: to have a mad time at the Mardi Gras. 8. (of wind, storms, etc.) furious in violence: A mad gale swept across the channel. 9. like mad,Informal.with great haste, impulsiveness, energy, or enthusiasm: She ran like mad to catch the bus. 10. mad as a hatter, completely insane.
—n. an angry or ill-tempered period, mood, or spell: The last time he had a mad on, it lasted for days.