Caucasian vs white man

Caucasian and white man both are nouns.

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

As nouns, white man is a hyponym of Caucasian; that is, white man is a word with a more specific, narrower meaning than Caucasian:

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

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

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