diagnostician vs specialist

diagnostician and specialist both are nouns.

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

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

Other hypernyms of diagnostician include medical specialist.

diagnostician (noun)	specialist (noun)
a doctor who specializes in medical diagnosis	an expert who is devoted to one occupation or branch of learning
	practices one branch of medicine