quack vs Dr.

quack and Dr. both are nouns.

Word	Noun	Adjective	Verb	Adverb
quack	Yes	Yes	Yes	No
Dr.	Yes	No	No	No

As nouns, Dr. is a hypernym of quack; that is, Dr. is a word with a broader meaning than quack:

quack: an untrained person who pretends to be a physician and who dispenses medical advice
Dr.: a licensed medical practitioner

Other hypernyms of quack include doc, doctor, MD, medico, physician, charlatan, mountebank.

quack (noun)	Dr. (noun)
the harsh sound of a duck	a licensed medical practitioner
an untrained person who pretends to be a physician and who dispenses medical advice	a person who holds Ph.D. degree (or the equivalent) from an academic institution

quack (adjective)	Dr. (adjective)
medically unqualified

quack (verb)	Dr. (verb)
act as a medical quack or a charlatan
utter quacking noises