1910年, 医学拉丁语, “最高级的弱智者之一”, 来自希腊语(Attic) mōron, mōros “愚蠢, 呆板, 迟钝, 愚蠢” 的中性词, 这个词的来源不确定. 前者与梵文 murah “idiotic” (见 moratorium) 的关系存疑. 拉丁文 morus “愚昧” 是希腊文的借词.
由美国弱智研究协会采用, 技术定义为“心智年龄在8岁至12岁之间的成年人;” 1922年起用作侮辱词, 后来从技术上放弃使用. 林奈斯曾提出 morisis “白痴”.
The feeble-minded may be divided into: (1) Those who are totally arrested before the age of three so that they show the attainment of a two-year-old child or less; these are the idiots. (2) Those so retarded that they become permanently arrested between the ages of three and seven; these are imbeciles. (3) Those so retarded that they become arrested between the ages of seven and twelve; these were formerly called feeble-minded, the same term that is applied to the whole group. We are now proposing to call them morons, this word being the Greek for “fool.” The English word “fool” as formerly used describes exactly this grade of child—one who is deficient in judgment or sense. [Henry H. Goddard, in “Journal of Proceedings and Addresses” of the National Education Association of the United States, July 1910]