(Australia) Eccentricity attributed to isolation from society, as in the outback.

(archaic) rabies

(historical) lunacy supposed to be caused by sleeping in full moonlight

(idiomatic) A well-thought-out reason for a person's seemingly illogical behavior.

(hyperbolic) The mentioned activity will cause frustration, anger, etc.

(Britain, New Zealand, informal) Completely insane.

A stock character in popular fiction; a bumbling scientist working on unlikely ways to save the world, or a villainous one bent on destroying it.

(uncountable, by ellipsis) Mad cow disease; bovine spongiform encephalopathy. / (countable) A cow afflicted with mad cow disease. / Used other than figuratively or idiomatically: see mad, cow.

(idiomatic) Extremely angry; furious to the point of outburst.

Alternative spelling of madman