Words related to ethnic
1580s, "form of speech peculiar to a people or place;" meaning "phrase or expression peculiar to a language" is from 1620s; from French idiome (16c.) and directly from Late Latin idioma "a peculiarity in language," from Greek idioma "peculiarity, peculiar phraseology" (Fowler writes that "A manifestation of the peculiar" is "the closest possible translation of the Greek word"), from idioumai "to appropriate to oneself," from idios "personal, private," properly "particular to oneself."
This is from PIE *swed-yo-, suffixed form of root *s(w)e-, pronoun of the third person and reflexive (referring back to the subject of a sentence), also used in forms denoting the speaker's social group, "(we our-)selves" (source also of Sanskrit svah, Avestan hva-, Old Persian huva "one's own," khva-data "lord," literally "created from oneself;" Greek hos "he, she, it;" Latin suescere "to accustom, get accustomed," sodalis "companion;" Old Church Slavonic svoji "his, her, its," svojaku "relative, kinsman;" Gothic swes "one's own;" Old Norse sik "oneself;" German Sein; Old Irish fein "self, himself").
[G]rammar & idiom are independent categories; being applicable to the same material, they sometimes agree & sometimes disagree about particular specimens of it; the most can be said is that what is idiomatic is far more often grammatical than ungrammatical, but that is worth saying, because grammar & idiom are sometimes treated as incompatibles .... [Fowler]
The Latin adjective also meant "of or belonging to the same nation," hence, as a noun, gentiles (plural) might mean "men of family; persons belonging to the same family; fellow countrymen, kinsmen," but also "foreigners, barbarians" (as opposed to Romans), those bound only by the Jus Gentium, the "law of nations," defined as "the law that natural reason establishes among all mankind and is followed by all peoples alike."
The Latin word then was used in the Vulgate to translate Greek ethnikos (see ethnic), from ta ethne "the nations," which translated Hebrew ha goyim "the (non-Jewish) nations" (see goy). Hence in Late Latin, after the Christianization of Rome, gentilis also could mean "pagans, heathens," as opposed to Christians. Based on Scripture, gentile also was used by Mormons (1847) and Shakers (1857) to refer to those not of their profession.