medical specialist vs physician

medical specialist and physician both are nouns.

Word	Noun	Adjective	Verb	Adverb
medical specialist	Yes	No	No	No
physician	Yes	No	No	No

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

Other hypernyms of medical specialist include doc, doctor, Dr., MD, medico.

medical specialist (noun)	physician (noun)
practices one branch of medicine	a licensed medical practitioner