specialist vs MD

specialist and MD both are nouns.

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

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

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

specialist (noun)	MD (noun)
an expert who is devoted to one occupation or branch of learning	a doctor's degree in medicine
practices one branch of medicine	a Mid-Atlantic state; one of the original 13 colonies, with capital Annapolis
	a licensed medical practitioner