A condition in which someone’s mind has not developed fully.
A state of arrested or incomplete development of mind. Mental sub-normality is essentially an administrative concept, describing the state of those whose intellectual powers have failed to develop to such an extent that they are in need of care and protection. This depends in part on social circumstances, for a person who is subnormal in a demanding culture may manage well in a simpler environment. It is also known as mental retardation, mental deficiency, and amentia.