executioner vs headman

executioner and headman both are nouns.

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

As nouns, headman is a hyponym of executioner; that is, headman is a word with a more specific, narrower meaning than executioner:

executioner: an official who inflicts capital punishment in pursuit of a warrant
headman: an executioner who beheads the condemned person

Other hyponyms of executioner include electrocutioner, hangman, headsman.

executioner (noun)	headman (noun)
an official who inflicts capital punishment in pursuit of a warrant	the head of a tribe or clan
	an executioner who beheads the condemned person