Probably from etho; a race (as of the same habit), i.e. A tribe; specially, a foreign (non-Jewish) one (usually, by implication, pagan) -- Gentile, heathen, nation, people.
see GREEK etho
1. a multitude (whether of men or of beasts) associated or living together; a company, troop, swarm: ἔθνος ἑταίρων, ἔθνος Ἀχαιων, ἔθνος λαῶν, Homer, Iliad; ἔθνος μελισσαων, 2, 87; μυιαων ἐθνεα, ibid. 469.
2. "a multitude of individuals of the same nature or genus (τό ἔθνος τό θῆλυ ἤ ἀρρεν, Xenophon, oec. 7, 26): πᾶν ἔθνος ἀνθρώπων, the human race, Acts 17:26 (but this seems to belong under the next entry).
3. race, nation: Matthew 21:43; Acts 10:35, etc.; ἔθνος ἐπί ἔθνος, Matthew 24:7; Mark 13:8: οἱ ἄρχοντες, οἱ βασιλεῖς τῶν ἐθνῶν, Matthew 20:25; Luke 22:25; used (in the singular) of the Jewish people, Luke 7:5; Luke 23:2; John 11:48, 50-53; John 18:35; Acts 10:22; Acts 24:2 ( 4. (τά ἔθνη, like הַגויִם in the O. T., foreign nations not worshipping the true God, pagans, Gentiles, (cf. Trench, § xcviii.): Matthew 4:15 (Γαλιλαία τῶν ἐθνῶν), 5. Paul uses τά ἔθνη even of Gentile Christians: Romans 11:13; Romans 15:27; Romans 16:4; Galatians 2:12 (opposite Galatians 2:13 to οἱ Ἰουδαῖοι, i. e. Jewish Christians), Galatians 2:14; Ephesians 3:1, cf. Ephesians 4:17 (Winers Grammar, § 59, 4 a.; Buttmann, 130 (114)).