An obsolescent term for mental retardation, particularly the severe, congenital type of defect in which the brain fails to develop. This type of mental retardation is also called primary mental deficiency. The term has never been widely used in the United States, but in Britain it is applied to all grades of mental deficiency. In Germany, on the other hand, it is applied to the acute confu- sional state which occurs in delirium. American psychologists and psychiatrists usually avoid the term because of the confusion that surrounds its use, and because it implies a total lack of intellect, which is rarely found.