gastroenterologist vs physician

gastroenterologist and physician both are nouns.

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

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

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

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

gastroenterologist (noun)	physician (noun)
a physician who specializes in diseases of the gastrointestinal tract	a licensed medical practitioner