British East Africa vs dominion

British East Africa and dominion both are nouns.

Word	Noun	Adjective	Verb	Adverb
British East Africa	Yes	No	No	No
dominion	Yes	No	No	No

As nouns, dominion is a hypernym of British East Africa; that is, dominion is a word with a broader meaning than British East Africa:

British East Africa: the former British territories of eastern Africa, including Kenya, Tanganyika, Uganda, and Zanzibar
dominion: a region marked off for administrative or other purposes

Other hypernyms of British East Africa include district, territorial dominion, territory.

British East Africa (noun)	dominion (noun)
the former British territories of eastern Africa, including Kenya, Tanganyika, Uganda, and Zanzibar	a region marked off for administrative or other purposes
	dominance or power through legal authority