brain surgeon vs surgeon

brain surgeon and surgeon both are nouns.

Word	Noun	Adjective	Verb	Adverb
brain surgeon	Yes	No	No	No
surgeon	Yes	No	No	No

As nouns, surgeon is a hypernym of brain surgeon; that is, surgeon is a word with a broader meaning than brain surgeon:

brain surgeon: someone who does surgery on the nervous system (especially the brain)
surgeon: a physician who specializes in surgery

Other hypernyms of brain surgeon include operating surgeon, sawbones.

brain surgeon (noun)	surgeon (noun)
someone who does surgery on the nervous system (especially the brain)	a physician who specializes in surgery