語源は不確かだが、元の意味は壊れた、破裂した、クレイジー舗装を参照、おそらく亀裂、破裂音から。また、心理学的な意味への拡張により、精神的断裂、狂気。
... there is little assurance in reconciled enemies: whose affections (for the most part) are like unto Glasse; which being once cracked, can neuer be made otherwise then crazed and vnsound. [John Hayward, "The Life and Raigne of King Henrie the IIII," 1599]