specialist vs physician

specialist and physician both are nouns.

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

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

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

specialist (noun)	physician (noun)
an expert who is devoted to one occupation or branch of learning	a licensed medical practitioner
practices one branch of medicine