Γεια σου Ιάκοβε
The Greek abbreviation Δρ comes from the Greek word "δόκτωρ". (The words "δόκτωρ" in Greek and "doctor" in English have the same Latin root. )
Δόκτωρ in Greek has two meanings:
1. Holder of a PhD Degree.
So, the eabbriviationcan Δρ can be used either for a person of any job who has a PhD degree or for a doctor.
Δρ Ιωάννης Παπαδόπουλος, Καρδιολόγος = Dr John Papadopoulos, cardiologist (Δρ indicates that he is a doctor)
Δρ Γεώργιος Παπαδόπουλος, καθηγητής Αρχαιολογίας = George Papadopoulos, professor of Archaeology (Δρ indicates that he has a PhD Degree)