Black African vs kaffir

Black African and kaffir both are nouns.

Word	Noun	Adjective	Verb	Adverb
Black African	Yes	No	No	No
kaffir	Yes	No	No	No

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

Other hyponyms of Black African include caffer, caffre, kafir.

Black African (noun)	kaffir (noun)
an African who is Black	an offensive and insulting term for any Black African
	important for human and animal food; growth habit and stem form similar to Indian corn but having sawtooth-edged leaves