general practitioner vs Dr.

general practitioner and Dr. both are nouns.

Word	Noun	Adjective	Verb	Adverb
general practitioner	Yes	No	No	No
Dr.	Yes	No	No	No

As nouns, Dr. is a hypernym of general practitioner; that is, Dr. is a word with a broader meaning than general practitioner:

general practitioner: a physician who is not a specialist but treats all illnesses
Dr.: a licensed medical practitioner

Other hypernyms of general practitioner include doc, doctor, MD, medico, physician.

general practitioner (noun)	Dr. (noun)
a physician who is not a specialist but treats all illnesses	a licensed medical practitioner
	a person who holds Ph.D. degree (or the equivalent) from an academic institution