tribal chief vs chieftain

tribal chief and chieftain both are nouns.

Word	Noun	Adjective	Verb	Adverb
tribal chief	Yes	No	No	No
chieftain	Yes	No	No	No

As nouns, tribal chief and chieftain are synonyms defined as:

Other synonyms of tribal chief include chief, headman.

tribal chief (noun)	chieftain (noun)
the head of a tribe or clan	the head of a tribe or clan
	the leader of a group of people