ethnic group vs ethnos

ethnic group and ethnos both are nouns.

Word	Noun	Adjective	Verb	Adverb
ethnic group	Yes	No	No	No
ethnos	Yes	No	No	No

As nouns, ethnic group and ethnos are synonyms defined as:

ethnic group and ethnos: people of the same race or nationality who share a distinctive culture

ethnic group (noun)	ethnos (noun)
people of the same race or nationality who share a distinctive culture	people of the same race or nationality who share a distinctive culture