Online Etymology Dictionary

so (adv.): Old English swa, swæ "in this way," from Proto-Germanic *swa (cf. Old Saxon, Middle Dutch, Old High German so, Old Norse sva, Danish saa, Swedish så, Old Frisian sa, Dutch zo, German so "so," Gothic swa "as"), from PIE reflexive pronomial stem *s(w)o- (cf. Greek hos "as," Old Latin suad "so," Latin se "himself").
The adverb so at the beginning of a sentence ('So I'll pay for it!'), probably of Yiddish origin, occurs frequently in conversation. [M.Pei, "Story of English," 1952]
So? as a term of dismissal is attested from 1886 (short for is that so?); so what as an exclamation of indifference dates from 1934. So-so "mediocre" is from 1520s; so-and-so is from 1596 meaning "something unspecified;" first recorded 1897 as a euphemistic term of abuse.
so long: parting salutation, 1860, of unknown origin, perhaps from a German idiom (cf. German parting salutation adieu so lange, the full sense of which probably is something like "farewell, whilst (we're apart)"), perhaps from Hebrew shalom (via Yiddish sholom). Some have noted a similarity to Scandinavian leave-taking phrases, cf. Norwegian Adjø så lenge, Farvel så lenge, Mor'n så lenge, literally "bye so long, farewell so long, morning so long;" and Swedish Hej så länge "good-bye for now," with så länge "for now" attested since 1850 according to Swedish sources. Most etymology sources seem to lean toward the German origin.

Earlier guesses that it was a sailors' corruption of a South Pacific form of Arabic salaam are not now regarded as convincing. "Dictionary of American Slang" also adds to the list of candidates Irish slán "safe," said to be used as a salutation in parting. The phrase seems to have turned up simultaneously in America, Britain, and perhaps Canada, originally among lower classes. First attested use is in title and text of the last poem in Whitman's "Leaves of Grass" in the 1860 edition.
An unknown sphere, more real than I dream'd, more direct, darts awakening rays about me -- So long!
Remember my words -- I may again return,
I love you -- I depart from materials;
I am as one disembodied, triumphant, dead.
Whitman's friend and fan William Sloane Kennedy, wrote in 1923:
The salutation of parting -- 'So long!' -- was, I believe, until recent years, unintelligible to the majority of persons in America, especially in the interior, and to members of the middle and professional classes. I had never heard of it until I read it in Leaves of Grass, but since then have quite often heard it used by the laboring class and other classes in New England cities. Walt wrote to me, defining 'so long' thus: "A salutation of departure, greatly used among sailors, sports, & prostitutes -- the sense of it is 'Till we meet again,' -- conveying an inference that somehow they will doubtless so meet, sooner or later." ... It is evidently about equivalent to our 'See you later.' The phrase is reported as used by farm laborers near Banff, Scotland. In Canada it is frequently heard; 'and its use is not entirely confined to the vulgar.' It is in common use among the working classes of Liverpool and among sailors at Newcastle-upon-Tyne, and in Dorsetshire. ... The London Globe suggests that the expression is derived from the Norwegian 'Saa laenge,' a common form of 'farewell,' au revoir. If so, the phrase was picked up from the Norwegians in America, where 'So long' first was heard. The expression is now (1923) often used by the literary and artistic classes.
so-called (adj.): 1650s, from so + call (v.). As a "sneer word" (Safire), from 1837.
soak (v.): Old English socian (related to sucan "to suck"), from Proto-Germanic *sukon (cf. West Flemish soken), from PIE root *seue- "to take liquid" (see sup (2)). Slang meaning "to overcharge" first recorded 1895. Related: Soaked; soaking.
soap (n.): Old English sape "soap" (originally a reddish hair dye used by Germanic warriors to give a frightening appearance), from West Germanic *saipo- "dripping thing, resin" (cf. Middle Low German sepe, West Frisian sjippe, Dutch zeep, Old High German seiffa, German seife "soap," Old High German seifar "foam," Old English sipian "to drip"), from PIE root *seib- "to pour out, drip, trickle" (cf. Latin sebum "tallow, suet, grease").

Romans and Greeks used oil to clean skin; the Romance language words for "soap" (cf. Italian sapone, French savon, Spanish jabon) are from Late Latin sapo (first mentioned in Pliny), which is a Germanic loan-word, as is Finnish saippua. The meaning "flattery" is recorded from 1853.
soap (v.): 1580s, from soap (n.). Related: Soaped; soaping.
soap opera (n.): 1939 (sponsors were often soap manufacturers), from earlier horse opera "a Western" (1927); shortened form soap first attested 1943.
soapbox (n.): also soap box, 1650s, "box for holding soap," later especially a wooden crate in which soap may be packed; from soap (n.) + box (n.). Typical of a makeshift stand for a public orator since at least 1907. Also used by children to make racing carts, cf. soap-box derby, annual race in Dayton, Ohio, which dates back to 1933.
soapstone (n.): 1680s, from soap (n.) + stone (n.). So called because it is occasionally used for cleaning.
soar (v.): late 14c., from Old French essorer "fly up, soar," from Vulgar Latin *exaurare "rise into the air," from Latin ex- "out" (see ex-) + aura "breeze, air" (see aura). Related: Soared; soaring.
sob (v.): c.1200, probably of imitative origin, related to Old English seofian "to lament," Old High German sufan "to draw breath," West Frisian sobje "to suck."

Related: Sobbed; sobbing. The noun is attested from late 14c. Sob story is from 1913. Sob sister "female journalist who writes sentimental stories or advice columns" is from 1912.
sobeit: 1580s, from so be it, a rare survival of the English subjunctive.
sober (adj.): c.1300, "grave, serious, solemn," from Old French sobre, from Latin sobrius "not drunk, temperate," from se- "without" + ebrius "drunk," of unknown origin. Sense of "moderate, temperate," especially "abstaining from strong drink" is first attested mid-14c.; meaning "not drunk at the moment" is from late 14c. The verb meaning "to become sober" is attested from 1820 (usually with up). Sobersides "sedate, serious-minded person" is recorded from 1705.
sobriety (n.): c.1400, "moderation in indulgence," from French sobrieté or directly from Latin sobrietas, from sobrius (see sober). Meaning "steadiness, gravity" is recorded from 1540s.
sobriquet (n.): 1640s, from French sobriquet "nickname," from Middle French soubriquet, literally "a chuck under the chin," of unknown origin (first element probably from Latin sub "under").
soccer (n.): 1889, socca, later socker (1891), soccer (1895), originally university slang (with jocular formation -er (3)), from a shortened form of Assoc., abbreviation of association in Football Association (as opposed to Rugby football); cf. rugger, but they hardly could have taken the first three letters of Assoc.
sociability (n.): late 15c.; see sociable + -ity.
sociable (adj.): 1550s, from Latin sociabilis "close, intimate," from sociare "to join, unite," from socius "companion" (see social).
social (adj.): c.1500 (implied in socially), "characterized by friendliness or geniality," also "allied, associated," from Middle French social (14c.), from Latin socialis "united, living with others," from socius "companion," probably originally "follower," and related to sequi "to follow" (cf. Old English secg, Old Norse seggr "companion," which seem to have been formed on the same notion; see sequel).

Meaning "living or liking to live with others, disposed to friendly intercourse" is attested from 1729. Meaning "pertaining to society as a natural condition of human life" first attested 1695, in Locke.

Social climber is from 1926; social work is 1890; social worker 1904. Social drink(ing) first attested 1976. Social studies as an inclusive term for history, geography, economics, etc., is attested from 1938. Social security "system of state support for needy citizens" is attested from 1908. Social butterfly is from 1910, in figurative reference to "flitting."

Social contract is from Rousseau. Social Darwinism attested from 1887. Social engineering attested from 1899. Social science is from 1811. In late 19c. newspapers, social evil is "prostitution." Social justice is attested by 1718; social network by 1971; social networking by 1984.
social (n.): "friendly gathering," 1870, from social (adj.).
socialisation (n.): chiefly British English spelling of socialization (see socialize); for spelling, see -ize.
socialism (n.): 1832, from French socialisme or from social + -ism. Cf. socialist. Apparently first in reference to Robert Owen's communes. "Pierre Leroux (1797-1871), idealistic social reformer and Saint-Simonian publicist, expressly claims to be the originator of the word socialisme" [Klein]. The word begins to be used in French in the modern sense c.1835.
socialist (n.): 1827, from French socialiste, in reference to the teachings of Comte de Saint-Simon, founder of French socialism. The word begins to be used in French in the modern sense c.1835. Socialista, with a different sense, was applied 18c. to followers and pupils of Dutch jurist Grotius (1583-1645).
Prison is a Socialist's Paradise, where equality prevails, everything is supplied and competition is eliminated. [Elbert Hubbard, "The Note Book," 1927]
socialistic (adj.): 1848, from socialist + -ic.
socialite (n.): 1928, probably a coinage among writers and editors at "Time" magazine, perhaps as a contraction of social light, in imitation of words in -ite (1).
sociality (n.): 1640s, from French socialité or directly from Latin socialitas, from socialis (see social).
socialization (n.): 1841, in reference to personal associations; 1884 in reference to socialism; noun of action from socialize.
socialize (v.): 1828, "to render social," from social (adj.). Meaning "to be sociable, to mingle" is recorded from 1895. Related: Socialized; socializing.
societal (adj.): 1898; see society + -al. Related: Societally.
society (n.): 1530s, "friendly association with others," from Old French societe, from Latin societatem (nominative societas), from socius "companion" (see social). Meaning "group of people living together in an ordered community" is from 1630s. Sense of "fashionable people and their doings" is first recorded 1823.
Socinian: 1640s, from Faustus Socinus, Latinized name of Fausto Sozzini (1539-1604), Italian theologian who denied the divinity of Christ, broke with the Church, and organized the Polish Brethren.
socio-: word-forming element from combining form of Latin socius "companion, associate" (see social (adj.)). Common in compounds since c.1880, e.g. sociobiology "study of the biological basis of social behavior" (1946).
socioeconomic (adj.): also socio-economic, 1883; see socio- + economic.
sociological (adj.): 1861; see sociology + -ical. Related: Sociologically.
sociology (n.): 1843, from French sociologie, a hybrid coined 1830 by French philosopher Isidore Auguste Comte (1798-1857), from Latin socius "associate" (see social) + Greek-derived suffix -logie (see -logy).
sociopath (n.): 1930, coined by psychologist G.E. Partridge from socio- on model of psychopath.
sociopolitical (adj.): also socio-political, 1884, from socio- + political.
sock (n.): Old English socc "light slipper," a West Germanic borrowing from Latin soccus "light low-heeled shoe," variant of Greek sykchos "a kind of shoe," perhaps from Phrygian or another Asiatic language. To knock the socks off (someone) "beat thoroughly" is recorded from 1845, American English colloquial. Teen slang sock hop is c.1950, from notion of dancing without shoes.
sock (v.2): "to stash (money) away as savings," 1942, American English, from the notion of hiding one's money in a sock (see sock (n.)).
sock (v.1): 1700, "to beat, hit," of uncertain origin. To sock it to (someone) first recorded 1877.
sockdolager (n.): 1830, "a decisive blow," fanciful formation from sock (v.) "hit hard;" also said to be a variant of doxology, on a notion of "finality." The meaning "something exceptional" is attested from 1838. Sockdologising was nearly the last word President Abraham Lincoln heard. During the performance of Tom Taylor's "Our American Cousin," assassin John Wilkes Booth (who knew the play well) waited for the line "Well, I guess I know enough to turn you inside out, you sockdologising old man-trap," and amid the noise as the audience laughed, Booth fired the fatal shot.
socket (n.): c.1300, "spearhead" (originally one shaped like a plowshare), from Anglo-French soket "spearhead" (mid-13c.), diminutive of Old French soc "plowshare," from Vulgar Latin *soccus, probably from a Gaulish source, cf. Welsh swch "plowshare," Middle Irish soc "plowshare," properly "hog's snout," cognate with Latin sus "swine;" see sow (n.) "female pig." Meaning "hollow part or piece for receiving and holding something" first recorded mid-15c.; anatomical sense is from c.1600; domestic electrical sense first recorded 1885. Socket wrench is attested from 1905.
socratic (adj.): 1630s, "of or pertaining to Greek philosopher Socrates" (469-399 B.C.E.), especially in reference to his method of eliciting truth by question and answer. His name is Greek Sokrates, literally "having safe might."
sod (n.1): "slice of earth with grass on it," early 15c., apparently from Middle Dutch sode "turf," Middle Low German sode, or Old Frisian satha "sod," all of uncertain origin. The (old) sod "Ireland" is from 1812.
sod (n.2): term of abuse, 1818, short for sodomite (see sodomy). British colloquial sod-all "nothing" is attested from 1958.
soda (n.): late 15c., "sodium carbonate," an alkaline substance extracted from certain ashes (now made artificially), from Italian sida (or Medieval Latin soda) "a kind of saltwort," from which soda is obtained, perhaps from Arabic suwwad, the name of a variety of saltwort exported from North Africa to Sicily in the Middle Ages, related to sawad "black," the color of the plant.

Washing soda (sodium carbonate) is commonly distinguished from baking soda (sodium bicarbonate). The meaning "carbonated water" is first recorded 1834, a shortening of soda water (1802). Soda fountain is from 1824; soda jerk first attested 1883. First record of soda pop is from 1873.
sodality (n.): "companionship, fellowship," c.1600, from Middle French sodalité, from Latin sodalitatem (nominative sodalitas) "companionship, a brotherhood," from sodalis "companion," related to suescere "to accustom" (see mansuetude). Especially of religious guilds in the Catholic Church.
sodden (adj.): Old English soden, strong past participle of seoþan "to cook, boil" (see seethe). Originally "boiled;" sense of "soaked" is first recorded 1820.
sodium (n.): metallic alkaline element, 1807, coined by English chemist Humphry Davy from soda; so called because the element was isolated from caustic soda (sodium hydroxide). The chemical symbol Na is from natrium, alternative name for the element proposed by Berzelius from natron, a name of a type of soda.
Sodom (n.): "any wicked or corrupt place," 1640s, from the morally corrupt city in ancient Palestine, said to have been destroyed, with neighboring Gomorrah, by fire from heaven (Gen. xviii-xix). From Hebrew s'dom, of unknown origin.