white man vs Caucasian

white man and Caucasian both are nouns.

Word	Noun	Adjective	Verb	Adverb
white man	Yes	No	No	No
Caucasian	Yes	Yes	No	No

As nouns, Caucasian is a hypernym of white man; that is, Caucasian is a word with a broader meaning than white man:

white man: a man who is White
Caucasian: a person of European descent with a light-skinned or pale complexion

Other hypernyms of white man include White, White person, adult male, man.

white man (noun)	Caucasian (noun)
a man who is White	a number of languages spoken in the Caucasus that are unrelated to languages spoken elsewhere
	a person of European descent with a light-skinned or pale complexion

white man (adjective)	Caucasian (adjective)
	of or relating to the geographical region of Caucasia
	of or relating to Caucasian people