white woman vs Caucasian

white woman and Caucasian both are nouns.

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

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

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

Other hypernyms of white woman include White, White person, adult female, woman.

white woman (noun)	Caucasian (noun)
a woman 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 woman (adjective)	Caucasian (adjective)
	of or relating to the geographical region of Caucasia
	of or relating to Caucasian people