Answers to Gospel Questions, Smith, 1:138-141; refer in this text to 3 Ne. 21:5-6
“Israel meant the literal descendants of Jacob and the twelve sons of Jacob, or house of Israel. The Gentiles, as the word literally means, were ‘The other people.’ … Eventually both of these words were enlarged in their scope to include land designation—the land where the Israelites lived, and the land where the Gentiles lived. Still a third meaning eventually developed, so that ‘Israel’ designated those who by covenant accept the true religion, and ‘Gentiles’ meant those who did not.” (Robert J. Matthews, Studies in Scripture, ed. by K. Jackson, 8: 168-171)
“After the Kingdom of Israel was destroyed and the Ten Tribes were led away into Assyrian captivity, those of the Kingdom of Judah called themselves Jews and designated all others as Gentiles. It is this concept that would have been taught to Lehi, Mulek and the other Jews who came to the Western Hemisphere to found the great Nephite and Lamanite civilizations. It is not surprising, therefore, to find the Book of Mormon repeatedly speaking of Jew and Gentile as though this phrase marked a division between all men; to find the United States described as a Gentile Nation (1 Ne. 13; 3 Ne. 21); and to find the promise that the Book of Mormon would come forth ‘by way of the Gentile’ (Title page of Book of Mormon; D&C 20:9).” (Bruce R. McConkie, Mormon Doctrine, p. 311)
“The literal descendants of Abraham (Hebrews) include [among others] the descendants of Jacob (Israelites), [and] Judah, (Jews), [Judah was the fourth born son of Jacob]… . The basic meaning of the word Gentile is ‘foreign,’ ‘other,’ or ‘non.’ Thus, to a Hebrew, a Gentile is a non-Hebrew; to an Israelite, a Gentile is a non-Israelite; and to a Jew, a Gentile is a non-Jew. In this sense, some Latter-day Saints have referred to those who are not members of the Church as Gentiles, even though the non-members might be Jews! The word Gentile might also be used in several different ways to refer to family, religious, political, or even geographical relationships. For example, a person might be considered an Israelite in a family or blood sense, but might be called a Gentile in a political or geographical sense because he lives in a land or nation that is primarily Gentile, or non-Israelitish.” (Daniel H. Ludlow, Ensign, Jan. 1991, pp. 51-52)