veterinarian vs MD

veterinarian and MD both are nouns.

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

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

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

veterinarian (noun)	MD (noun)
a doctor who practices veterinary medicine	a doctor's degree in medicine
	a Mid-Atlantic state; one of the original 13 colonies, with capital Annapolis
	a licensed medical practitioner