mental disease n: an abnormal mental condition that interferes with mental or emotional processes and internal behavioral control and that is not manifest only in repeated criminal or antisocial conduct
: mental illness NOTE: Mental disease and mental illness are in general use synonymous, but mental disease has developed a settled meaning in criminal law while mental illness is often explained or defined by reference to the medical community's understanding of the term.
Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.