operating surgeon vs Dr.

operating surgeon and Dr. both are nouns.

Word	Noun	Adjective	Verb	Adverb
operating surgeon	Yes	No	No	No
Dr.	Yes	No	No	No

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

Other hypernyms of operating surgeon include doc, doctor, MD, medico, physician.

operating surgeon (noun)	Dr. (noun)
a physician who specializes in surgery	a licensed medical practitioner
	a person who holds Ph.D. degree (or the equivalent) from an academic institution