Involutional insanity
Defined in 1 dictionary — Black's (1910)
Black's Law Dictionary
Henry Campbell Black, M.A. · 1910
That which sometimes accompanies the "involution" of the physical structure and physiology of the individual, the reverse of their "evolution," hence practically equivalent to the imbecility of old age or senile dementia.
Defined under Insanity in Black's Law Dictionary.