crazy: [16] Crazy originally meant literally ‘cracked’ (a sense preserved in the related crazed). This soon came to be extended metaphorically to ‘frail, ill’ (as in Shakespeare’s ‘some better place, fitter for sickness and crazy age’, 1 Henry VI), and thence to ‘mentally unbalanced’. It was derived from the verb craze [14], which was probably borrowed from an unrecorded Old Norse verb *krasa ‘shatter’ (likely source, too, of French écraser ‘crush, smash’).
1570s, "diseased, sickly," from craze + -y (2). Meaning "full of cracks or flaws" is from 1580s; that of "of unsound mind, or behaving as so" is from 1610s. Jazz slang sense "cool, exciting" attested by 1927. To drive (someone) crazy is attested by 1873. Phrase crazy like a fox recorded from 1935. Crazy Horse, Teton Lakhota (Siouan) war leader (d.1877) translates thašuka witko, literally "his horse is crazy."
