gastroenterologist vs MD

gastroenterologist and MD both are nouns.

Word	Noun	Adjective	Verb	Adverb
gastroenterologist	Yes	No	No	No
MD	Yes	No	No	No

As nouns, MD is a hypernym of gastroenterologist; that is, MD is a word with a broader meaning than gastroenterologist:

gastroenterologist: a physician who specializes in diseases of the gastrointestinal tract
MD: a licensed medical practitioner

Other hypernyms of gastroenterologist include doc, doctor, Dr., medico, physician.

gastroenterologist (noun)	MD (noun)
a physician who specializes in diseases of the gastrointestinal tract	a doctor's degree in medicine
	a Mid-Atlantic state; one of the original 13 colonies, with capital Annapolis
	a licensed medical practitioner