AryanyoudaoicibaDictYouDict
c. 1600, as a term in classical history, from Latin Arianus, Ariana, from Greek Aria, Areia, names applied in classical times to the eastern part of ancient Persia and to its inhabitants. Ancient Persians used the name in reference to themselves (Old Persian ariya-), hence Iran. Ultimately from Sanskrit arya- "compatriot;" in later language "noble, of good family."

Also the name Sanskrit-speaking invaders of India gave themselves in the ancient texts, from which early 19c. European philologists (Friedrich Schlegel, 1819, who linked the word with German Ehre "honor") applied it to the ancient people we now call Indo-Europeans (suspecting that this is what they called themselves); this use is attested in English from 1851. The term fell into the hands of racists, and in German from 1845 it was specifically contrasted to Semitic (Lassen).

German philologist Max Müller (1823-1900) popularized the term in his writings on comparative linguistics, recommending it as the name (replacing Indo-European, Indo-Germanic, Caucasian, Jshortened) for the group of related, inflected languages connected with these peoples, mostly found in Europe but also including Sanskrit and Persian. Arian was used in this sense from 1839 (and is more philologically correct), but this spelling caused confusion with Arian, the term in ecclesiastical history.

Gradually replaced in comparative linguistics c. 1900 by Indo-European, except when used to distinguish Indo-European languages of India from non-Indo-European ones. Used in Nazi ideology to mean "member of a Caucasian Gentile race of Nordic type." As an ethnic designation, however, it is properly limited to Indo-Iranians (most justly to the latter) and has fallen from general academic use since the Nazi era.
genocide (n.)youdaoicibaDictYouDict
1944, apparently coined by Polish-born U.S. jurist Raphael Lemkin (1900-1959) in his work "Axis Rule in Occupied Europe" [p.19], in reference to Nazi extermination of Jews, literally "killing a tribe," from Greek genos "race, kind" (see genus) + -cide. The proper formation would be *genticide.
Generally speaking, genocide does not necessarily mean the immediate destruction of a nation, except when accomplished by mass killings of all members of a nation. It is intended rather to signify a coordinated plan of different actions aimed at the destruction of essential foundations of the life of national groups, with the aim of annihilating the groups themselves. [Lemkin]
Earlier in a similar sense was populicide (1799), from French populicide, by 1792, a word from the Revolution. This was taken into German, as in Völkermeuchelnden "genocidal" (Heine), which was Englished 1893 as folk-murdering. Ethnocide is attested from 1974 in English (1970 in French).
slang (n.)youdaoicibaDictYouDict
1756, "special vocabulary of tramps or thieves," later "jargon of a particular profession" (1801), of uncertain origin, the usual guess being that it is from a Scandinavian source, such as Norwegian slengenamn "nickname," slengja kjeften "to abuse with words," literally "to sling the jaw," related to Old Norse slyngva "to sling." But OED, while admitting "some approximation in sense," discounts this connection based on "date and early associations." Liberman also denies it, as well as any connection with French langue (or language or lingo). Rather, he derives it elaborately from an old slang word meaning "narrow piece of land," itself of obscure origin. Century Dictionary says "there is no evidence to establish a Gipsy origin." Sense of "very informal language characterized by vividness and novelty" first recorded 1818.
[S]lang is a conscious offence against some conventional standard of propriety. A mere vulgarism is not slang, except when it is purposely adopted, and acquires an artificial currency, among some class of persons to whom it is not native. The other distinctive feature of slang is that it is neither part of the ordinary language, nor an attempt to supply its deficiencies. The slang word is a deliberate substitute for a word of the vernacular, just as the characters of a cipher are substitutes for the letters of the alphabet, or as a nickname is a substitute for a personal name. [Henry Bradley, from "Slang," in "Encyclopedia Britannica," 11th ed.]
A word that ought to have survived is slangwhanger (1807, American English) "noisy or abusive talker or writer."