The word Gentiles (plural of Gentile) comes from the Hebrew word Goyim, meaning the non-Jewish peoples of the world. However, there is more to the story. Please, allow me to explain.
When God called Abram to go to the land that one day would be called the Land of Israel, He promised him that he would become a great nation (ג֣וֹי גָּד֔וֹל), pronounced goy gadol. However, God’s promise to Abram also included other nations. God said that through Abram all the other families of the earth (מִשְׁפְּחֹ֥ת הָאֲדָמָֽה) would be blessed (Gen.12:1-3).
Adam, pronounced Adam (אָדָ֕ם), and the earth, pronounced Adama (אֲדָמָֽה) from which Adam originated, have the same Hebrew root. This speaks of a strong connection. When describing God’s promise to Abram, Moses purposely used the word for the nations of the world that connected them to Adam. He called them the families of the earth, pronounced mishpachot haadama (מִשְׁפְּחֹ֥ת הָאֲדָמָֽה).
When we come to the Septuagint (Greek translation of the Hebrew Bible) and to the New Testament, both authored in what can be best called Koine Judeo-Greek, we see that the same Hebrew word goyim (גּוֹיִם) is accurately translated as ἔθνη, pronounced as ethnei. This sounds familiar to us because it is from this word that our English words for “ethnicity” and “ethnic” are derived.
It is not until these Hebrew and Greek words are translated into Latin by such words as Gentes and Gentilis that the process of transforming the “nations” into “gentiles” in the English language formally begins.