poor white trash vs have-not

poor white trash and have-not both are nouns.

Word	Noun	Adjective	Verb	Adverb
poor white trash	Yes	No	No	No
have-not	Yes	No	No	No

As nouns, have-not is a hypernym of poor white trash; that is, have-not is a word with a broader meaning than poor white trash:

poor white trash: (slang) an offensive term for White people who are impoverished
have-not: a person with few or no possessions

Other hypernyms of poor white trash include Caucasian, White, White person, poor person.

poor white trash (noun)	have-not (noun)
(slang) an offensive term for White people who are impoverished	a person with few or no possessions