Boyd’s Bible Dictionary:
(dwellers on the heath). All except Jews (Psa. 2:1). Nonbeliever (Matt. 18:17).
Concise Bible Dictionary:
The Hebrew word goi is also translated “Gentiles,” and “people,” and very often “nations:” it is used in contrast to Israel irrespective of those designated being civilized or not. All the nations were idolaters, but this is not implied in the word goi, nor in the ἔθνος of the New Testament, which is more frequently translated “nations” and “Gentiles.” In Matthew 17 ἐθνικός has a peculiar application: if an offending brother will not hear the church, the injunction is “let him be unto thee as an heathen man and a publican,” that is, as an outsider, the heathen being outside the privileges of Israel, as one to be avoided (compare Rom. 16:17; 2 Thess. 3:6,14).