chieftain vs headman

chieftain and headman both are nouns.

Word	Noun	Adjective	Verb	Adverb
chieftain	Yes	No	No	No
headman	Yes	No	No	No

As nouns, chieftain and headman are synonyms defined as:

Other synonyms of chieftain include chief, tribal chief.

chieftain (noun)	headman (noun)
the head of a tribe or clan	the head of a tribe or clan
the leader of a group of people	an executioner who beheads the condemned person