Doctor means teacher in Latin. It has been used continuously as an honored academic title for over a millennium in Europe, where it dates back to the rise of the university. This use spread to the Americas, former European colonies, and is now prevalent in most of the world. As a prefix – “Dr” – its primary designation is a person who has obtained a doctorate — that is, an advanced university degree whose completion involves extensive research.
However, in the last two centuries of popular use in English-speaking and many other countries, the noun doctor has come to be used widely to refer to physicians (medical doctors), who are also granted use of the prefix as a courtesy title, whether or not they hold doctorates. The primary medical qualification in the UK and in many Commonwealth Countries is the degree of 'Bachelor of Medicine and Bachelor of Surgery' (MB BS, MB ChB, BM BCh or MB BChir, depending on the University granting the award). After qualification, medical practitioners may then read for the postgraduate research degree of 'Doctor of Medicine'.
Medical usage of the noun doctor
In United States and Canadian parlance, the noun doctor is most often used for all forms of physicians and surgeons, including internists, pediatricians, gynecologists, and all other surgical and nonsurgical specialists who hold M.D. degrees and practice medicine of any form. It is also used in this sense for osteopathic physicians (whose medical degree is D.O.). In a specific context or setting that does not include physicians, doctor is sometimes used as a noun to refer to a chiropractor, veterinarian, dentist, optometrist, podiatrist, pharmacist, or clinical psychologist (whose degrees are usually D.C., D.V.M., D.D.S. , O.D., D.P.M. , PharmD , Ph.D.), though less often in a context which includes physicians.
In the United Kingdom, Australia, and other areas whose culture was more recently linked to the United Kingdom, within medical circles the title Doctor generally applies to medically qualified individuals. However, those who are Members or Fellows of the Royal College of Surgeons for historic reasons prefer to be addressed as Mr, Mrs, Ms or Miss.
There are many other countries, such as France, where doctor nearly always is synonymous with medical doctor.
In other countries like Germany, Switzerland, Austria, there are ten thousands of doctors in law, economics, philosophy, chemistry, and so on.
Academic doctorates and usage of Doctor as a title of address
Although medical doctors and some other health professionals with the above medical degrees are addressed as Doctor (e.g., Doctor Smith or Dr Smith), medical degrees are not usually doctorates, except in the USA, where they are considered first-professional (as opposed to research-oriented) doctorates.
The most advanced academic degrees in any discipline, including the medical disciplines, are referred to as doctorates and represent the highest earned degree in a given area of the sciences or humanities. The most common of these is the Ph.D., but there are many other research-oriented doctorates with different designations. (See: doctorate.) In much of the world, holders of doctoral degrees are generally addressed as Doctor. In the USA, however, while the Juris Doctor or J.D. is indeed a professional doctorate, by custom and legal convention lawyers do not use the title of doctor. Laywers who hold another doctorate such as the J.S.D. (Doctor of Juristic Science), L.Sc.D. (Doctor of the Science of Law), Th.D. (Doctor of Theology, or the LL.D. (Doctor of Laws) may use the title of doctor. In an academic setting, where the educational background of the individual is of course salient, doctor is the term of address and title used by holders of a doctoral degree unless the holder has been appointed a professor, since this title usually supersedes the title doctor. Academics below the rank of professor who do not hold a doctoral degree are referred to as Mr, Mrs, Miss or Ms.
It is also true, however, that the usage of doctor as a title also varies by country and culture. While the title Doctor (abbreviated Dr) is used in the United States, the UK and Germany for most people holding a doctorate, in some other countries, such as France, it is generally not used except for physicians and thus has become a synonym for "physician". In certain countries, for members of certain professions, the title of doctor may be used even when the academic qualification of doctorate is not held: for instance, in Italy, for holders of a Laurea .
In Roman Catholicism, a Doctor of the Church is an eminent theologian (e.g. Thomas Aquinas) from whose teachings the whole Christian Church is held to have derived great advantage. This is not an academic title but reflects the most ancient sense of the word as "teacher".
"Doctor" is an undressing game played by children.