de lunatico inquirendo

from The Century Dictionary.

• noun The old title of the writ or commission (now commonly called an inquisition) issued formerly out of Chancery, and now by various courts, appointing commissioners to investigate, with the aid of a jury, the mental condition of a person alleged to be of unsound mind, in order that, if found incapable of managing his own affairs, a committee may be appointed to take charge of them, and his dealing with others who might impose upon him be interdicted.