radiologist vs specialist

radiologist and specialist both are nouns.

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

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

radiologist: a medical specialist who uses radioactive substances and X-rays in the treatment of disease
specialist: practices one branch of medicine

Other hypernyms of radiologist include medical specialist.

radiologist (noun)	specialist (noun)
a medical specialist who uses radioactive substances and X-rays in the treatment of disease	an expert who is devoted to one occupation or branch of learning
	practices one branch of medicine