Indian chief vs sachem

Indian chief and sachem both are nouns.

Word	Noun	Adjective	Verb	Adverb
Indian chief	Yes	No	No	No
sachem	Yes	No	No	No

As nouns, sachem is a hyponym of Indian chief; that is, sachem is a word with a more specific, narrower meaning than Indian chief:

Indian chief: the leader of a group of Native Americans
sachem: a chief of a North American tribe or confederation (especially an Algonquian chief)

Other hyponyms of Indian chief include sagamore.

Indian chief (noun)	sachem (noun)
the leader of a group of Native Americans	a chief of a North American tribe or confederation (especially an Algonquian chief)
	a political leader (especially of Tammany Hall)