ethnic vs heathen

ethnic and heathen both are nouns.

Word	Noun	Adjective	Verb	Adverb
ethnic	Yes	Yes	No	No
heathen	Yes	Yes	No	No

As adjectives, ethnic and heathen are synonyms defined as:

ethnic and heathen: not acknowledging the God of Christianity and Judaism and Islam

Other synonyms of ethnic include heathenish, pagan.

ethnic (noun)	heathen (noun)
a person who is a member of an ethnic group	a person who does not acknowledge your god

ethnic (adjective)	heathen (adjective)
not acknowledging the God of Christianity and Judaism and Islam	not acknowledging the God of Christianity and Judaism and Islam
denoting or deriving from or distinctive of the ways of living built up by a group of people