surgeon vs neurosurgeon

surgeon and neurosurgeon both are nouns.

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

As nouns, neurosurgeon is a hyponym of surgeon; that is, neurosurgeon is a word with a more specific, narrower meaning than surgeon:

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

Other hyponyms of surgeon include amputator, cosmetic surgeon, plastic surgeon, brain surgeon.

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