Uncle Tom vs Black person

Uncle Tom and Black person both are nouns.

Word	Noun	Adjective	Verb	Adverb
Uncle Tom	Yes	No	No	No
Black person	Yes	No	No	No

As nouns, Black person is a hypernym of Uncle Tom; that is, Black person is a word with a broader meaning than Uncle Tom:

Uncle Tom: (ethnic slur) offensive and derogatory name for a Black man who is abjectly servile and deferential to Whites
Black person: a person with dark skin who comes from Africa (or whose ancestors came from Africa)

Other hypernyms of Uncle Tom include African-American, Black, Negro, Negroid, blackamoor.

Uncle Tom (noun)	Black person (noun)
a servile black character in a novel by Harriet Beecher Stowe	a person with dark skin who comes from Africa (or whose ancestors came from Africa)
a servile black character in a novel by Harriet Beecher Stowe
(ethnic slur) offensive and derogatory name for a Black man who is abjectly servile and deferential to Whites