geriatrician vs specialist

geriatrician and specialist both are nouns.

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

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

Other hypernyms of geriatrician include medical specialist.

geriatrician (noun)	specialist (noun)
a specialist in gerontology	an expert who is devoted to one occupation or branch of learning
	practices one branch of medicine