sachem vs Indian chief

sachem and Indian chief both are nouns.

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

As nouns, Indian chief is a hypernym of sachem; that is, Indian chief is a word with a broader meaning than sachem:

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

Other hypernyms of sachem include Indian chieftain.

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