gastroenterologist vs doc

gastroenterologist and doc both are nouns.

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

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

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

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

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