Black man vs boy

Black man and boy both are nouns.

Word	Noun	Adjective	Verb	Adverb
Black man	Yes	No	No	No
boy	Yes	No	No	No

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

Black man (noun)	boy (noun)
a man who is Black	a youthful male person
	(ethnic slur) offensive and disparaging term for Black man
	a friendly informal reference to a grown man
	a male human offspring