From The Art and Popular Culture Encyclopedia
Doctor is an academic title that originates from the Latin word of the same spelling and meaning. The word is originally an agentive noun of the Latin verb Template:Lang Template:IPA-la 'to teach'. It has been used as an academic title in Europe since the 13th century, when the first doctorates were awarded at the University of Bologna and the University of Paris.
Having become established in European universities, this usage spread around the world. Contracted "Dr" or "Dr.", it is used as a designation for a person who has obtained a doctorate (e.g., PhD). In many parts of the world it is also used by medical practitioners, regardless of whether they hold a doctoral-level degree.