DR.

Doctor (gen.: doctoris) means teacher in Latin and is a contraction of the Greek διδάκτωρ, didaktōr, teacher, from the verb διδάσκειν, didaskein, to teach. 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 — abbreviated "Dr"— its primary designation is a person who has obtained a  doctorate (that is, a doctoral degree), which is the highest rank of academic degree awardable. Doctoral degrees may be "research doctorates", awarded on the basis of competency in research, or "taught doctorates" (also called "professional doctorates", because they are invariably awarded in professional subjects), awarded on the basis of coursework and adjunct requirements (if any) successfully completed by the conferee.
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Noun
1. a person who holds Ph.D. degree from an academic institution; "she is a doctor of philosophy in physics"
(synonym) doctor
(hypernym) scholar, scholarly person, student
2. a licensed medical practitioner; "I felt so bad I went to see my doctor"
(synonym) doctor, doc, physician, MD, medico
(hypernym) medical practitioner, medical man
(hyponym) abortionist
(member-holonym) doctor-patient relation

Ph.D.

= Doctor (Dr.), doctor (MD).
Nota: Licenciado en medicina.
Ex: He is the recipient of the Margaret Man Citation, the Beta Phi Award for good teaching and the honorary Doctor of Laws from UCLA.
Ex: This programme aims to put doctors and nurses back in the driving seat in managing their resources and information.

Doctor