allergist vs MD

allergist and MD both are nouns.

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

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

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

allergist (noun)	MD (noun)
a physician skilled in the diagnosis and treatment of allergies	a doctor's degree in medicine
	a Mid-Atlantic state; one of the original 13 colonies, with capital Annapolis
	a licensed medical practitioner