ethnarch vs ruler

ethnarch and ruler both are nouns.

Word	Noun	Adjective	Verb	Adverb
ethnarch	Yes	No	No	No
ruler	Yes	No	No	No

As nouns, ruler is a hypernym of ethnarch; that is, ruler is a word with a broader meaning than ethnarch:

ethnarch: the ruler of a province (as in the Roman Empire and Byzantine Empire) or certain religious rulers with secular authority
ruler: a person who rules or commands

Other hypernyms of ethnarch include swayer.

ethnarch (noun)	ruler (noun)
the ruler of a province (as in the Roman Empire and Byzantine Empire) or certain religious rulers with secular authority	measuring stick consisting of a strip of wood or metal or plastic with a straight edge that is used for drawing straight lines and measuring lengths
	a person who rules or commands