sui iuris (law) in one’s own right (used in law to indicate the ability to govern one’s own legal affairs and to be autononous)
in loco parentis (law) in the place of a parent (used to indicate the authority and responsibility of teachers, coaches, and administrators in a school)
cui bono? (law) for whose good? (used in a legal setting to help identify motive by determining who would benefit from a crime).