allergist vs physician

allergist and physician both are nouns.

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

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

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

allergist (noun)	physician (noun)
a physician skilled in the diagnosis and treatment of allergies	a licensed medical practitioner