GP vs doc

GP and doc both are nouns.

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

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

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

GP (noun)	doc (noun)
a physician who is not a specialist but treats all illnesses	a licensed medical practitioner