Nguni vs Zulu

Nguni and Zulu both are nouns.

Word	Noun	Adjective	Verb	Adverb
Nguni	Yes	No	No	No
Zulu	Yes	No	No	No

As nouns, Zulu is a hyponym of Nguni; that is, Zulu is a word with a more specific, narrower meaning than Nguni:

Nguni: a group of southern Bantu languages
Zulu: a Bantu language of considerable literary importance in southeastern Africa

Other hyponyms of Nguni include Matabele, Ndebele, Swazi, Swazi language, Xhosa, Xhosa language, Zulu language.

Nguni (noun)	Zulu (noun)
a group of southern Bantu languages	a Bantu language of considerable literary importance in southeastern Africa
	a community of Negroid people in eastern South Africa
	a member of the tall Negroid people of eastern South Africa; some live in KwaZulu-Natal under the traditional clan system but many now work in the cities