Although it has become less common, the word “Gentile” was once a standard way to refer to non-Jews. A long time ago, however, it was a Christian term for pagans. Marilyn Cooper explains:
Gentile came into the English language by way of the 4th-century Vulgate, the Roman Catholic Church’s authorized Latin translation of the Hebrew and Christian Bibles. In the Vulgate, St. Jerome translated the biblical word goy . . . and the Greek word ethne into the Latin term gentilis, which means “nation” or “people.” . . . [I]n the 17th-century King James Bible, . . . gentilis was anglicized into Gentile, as in I Corinthians 10:32: “Give none offence, neither to the Israelites, nor to the Gentiles, nor to the Church of God.”
For the next two centuries, gentile mainly referred to those who were not of an Abrahamic monotheistic religion—that is, someone who was not a Jew, a Muslim, or a Christian. . . . This began to change after the Protestant Reformation and the subsequent century of religious wars in Europe caused the Christian Church in the West to splinter into innumerable denominations. With widespread disagreement about who should be called a Christian, a neutral umbrella term was needed. Gentile filled the void.
From this period until the early 20th century, Gentile was most often used by Christians, usually in the context of missionizing activities or when writing about Old Testament texts.
Read more on Moment: http://www.momentmag.com/jewish-word-gentile/