Doctor comes from latin (from the verb docere - to teach) and basically means teacher, or someone with enough knowledge in a field to teach. The term is still used as an academic title, but in different way in different countries. For example, while in english speaking countries ot is used for someone who completed their PhD (phylosophæ doctorate), so someone with enough knowledge to do research and teach to an academic level, in Italy the title "dottore" is given to any who got a degree, even a Bachelor's, so a physician is a doctor in medicine because they graduated in medicine.