extern vs Dr.

extern and Dr. both are nouns.

Word	Noun	Adjective	Verb	Adverb
extern	Yes	No	No	No
Dr.	Yes	No	No	No

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

extern: a nonresident doctor or medical student; connected with a hospital but not living there
Dr.: a licensed medical practitioner

Other hypernyms of extern include doc, doctor, MD, medico, physician.

extern (noun)	Dr. (noun)
a nonresident doctor or medical student; connected with a hospital but not living there	a licensed medical practitioner
	a person who holds Ph.D. degree (or the equivalent) from an academic institution