Online Etymology Dictionary

slacker (n.): popularized 1994, but the meaning "person who shirks work" dates to 1897; agent noun from slack (v.). In early use also slackster (1901). Compare Old English sleacornes "laziness," which is not, however, an agent noun. Related: Slackerly; slackerish.
slackly (adv.): Old English slæclice; see slack (adj.) + -ly (2).
slackness (n.): Old English slæcnes "slowness, remissness, laziness;" see slack (adj.) + -ness.
slag (n.): "refuse from smelting," 1550s, from Middle Low German slagge (German Schlacke) "splinter flying off when metal is struck," related to Old High German slahan "to strike, slay" (see slay (v.)).
slag (v.): "denigrate," by 1971, from slag (n.) in a secondary sense of "worthless person" (1788). Related: Slagged; slagging.
slain (adj.): early 13c., from Old English (ge)slegen, past participle of slean (see slay (v.)). The noun meaning "those who have been slain" is attested from mid-14c.
slake (v.): late Old English sleacian, slacian "become slack or remiss; slacken an effort" (intransitive); "delay, retard" (transitive), from slæc "lax" (see slack (adj.)). Transitive sense of "make slack" is from late 12c. Sense of "allay, diminish in force, quench, extinguish" (in reference to thirst, hunger, desire, wrath, etc.) first recorded early 14c. via notion of "make slack or inactive." Related: Slaked; slaking.
slalom (n.): 1921, from Norwegian slalam "skiing race," literally "sloping track," from sla "slope" + lam "track" (related to Norwegian laan "a row of houses;" compare lane).
slam (n.1): 1670s, "a severe blow," probably from a Scandinavian source (compare Norwegian slamre, Swedish slemma "to slam, bang") of imitative origin. Meaning "a violent closing of a door" is from 1817. Meaning "an insult, put-down" is from 1884. Slam-bang recorded by 1806 (also slap-bang, 1785). Slam-dunk is from 1976; early use often in reference to Julius Erving. Slam-dance is attested by 1987 (slam by itself in this sense is recorded from 1983).
slam (n.2): "a winning of all tricks in a card game," 1660s, earlier the name of a card game (also called ruff), 1620s, used especially in whist, of obscure origin. Grand slam in bridge first recorded 1892; earlier in related card games from 1814; figurative sense of "complete success" is attested from 1920; in baseball sense from 1935.
slam (v.): 1690s, "to beat, slap;" 1775 as "to shut with force," from slam (n.1). Meaning "throw or push with force" is from 1870. Meaning "say uncomplimentary things about" is from 1916. Related: Slammed; slamming.
slammer (n.): "jail, prison," 1952, perhaps from earlier U.S. slang sense of "door" (by 1943), agent noun from slam (v.). As "one who slams," from 1892.
slander (n.): late 13c., "state of impaired reputation, disgrace or dishonor;" c. 1300, "a false tale; the fabrication and dissemination of false tales," from Anglo-French esclaundre, Old French esclandre "scandalous statement," alteration ("with interloping l" [Century Dictionary]) of escandle, escandre "scandal," from Latin scandalum "cause of offense, stumbling block, temptation" (see scandal). From late 14c. as "bad situation, evil action; a person causing such a state of affairs."
slander (v.): c. 1300, from Anglo-French esclaundrer, Old French esclandrer, from esclandre (see slander (n.)). Related: Slandered; slandering; slanderer.
slanderous (adj.): early 15c., from slander + -ous. Related: Slanderously; slanderousness.
slang (n.): 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."
slangy (adj.): 1822, from slang (n.) + -y (2). Related: Slanginess. Slangular (1852) also was tried.
slant (v.): 1520s, "to strike obliquely" (against something), alteration of slenten "slip sideways" (c. 1300), perhaps via a Scandinavian source (compare Swedish slinta "to slip," Norwegian slenta "to fall on one side"), from Proto-Germanic *slintanan. Intransitive sense of "to slope, to lie obliquely" is first recorded 1690s; transitive sense of "to give a sloping direction to" is from 1805. Related: Slanted; slanting. As an adverb from late 15c.; as an adjective from 1610s. Slant rhyme attested from 1944.
slant (n.): 1650s, "an oblique direction or plane" (originally of landforms), from slant (v.). Meaning "a way of regarding something" is from 1905. Derogatory slang sense of "a slant-eyed Asian person" is recorded from 1943, from earlier slant-eyes (1929).
slantways (adv.): 1826, from slant (n.) + way (n.) + adverbial genitive -s.
slap (v.): late 15c., "strike with the open hand," from slap (n.). As an adverb, 1670s, "suddenly;" 1829, "directly." Related: Slapped; slapping.
slap (n.): mid-15c., probably of imitative origin, similar to Low German slappe, German Schlappe. Figurative meaning "insult, reprimand" is attested from 1736. Slap-happy (1936) originally meant "punch-drunk." Slap on the wrist "very mild punishment" dates from 1914.
slapdash (adv.): 1670s, from slap (v.) + dash (v.). As an adjective, "dashing, offhand, careless," from 1792. As a noun, "rough-coat, coarse plaster," from 1796.
slapper (n.): "large or impressive person or thing," 1781, agent noun from slap (v.). Also see whopper.
slapshot (n.): in ice hockey, 1942, from slap (v.) + shot (n.).
slapstick (n.): also slap-stick, originally (1896) a device consisting of two sticks fastened together so as to slap loudly when a clown or actor hits somebody with it, or to make a sound-effect offstage; from slap and stick (n.). As an adjective by 1906. Meaning "farcical physical comedy, horseplay" (1916) is short for slapstick comedy or humor.
slash (v.): 1540s, "to cut with a stroke of a blade or whip;" 1650s, "to strike violently," perhaps from Middle French esclachier "to break," variant of esclater "to break, splinter" (see slat). Meaning "to clear land" (of trees) is from 1821, American English. In reference to prices, it is attested from 1906. Related: Slashed; slashing. Slash-and-burn for a method of clearing forest for cultivation is from 1919.
slash (n.): "a cutting stroke with a weapon," 1570s, from slash (v.); sense of "slit in a garment" is from 1610s; that of "open tract in a forest" is first attested 1825, American English. As a punctuation mark in writing or printing, it is recorded from 1961.
slasher (n.): 1550s, "a bully, a fighter;" 1815, "weapon for slashing," agent noun from slash (v.). As "violent movie" by 1978.
slat (n.): late 14c., earlier sclat (c. 1300), "a roofing slate, a thin, flat stone," from Old French esclat "split piece, chip, splinter" (Modern French éclat), back-formation from esclater "to break, splinter, burst," probably from Frankish *slaitan "to tear, slit" or some other Germanic source (compare Old High German slizan, Old English slitan; see slit (v.)). Meaning "long, thin, narrow piece of wood or metal" attested from 1764.
slate (n.): mid-14c., from Old French esclate, fem. of esclat "split piece, splinter" (Modern French éclat; see slat), so called because the rock splits easily into thin plates. As an adjective, 1510s. As a color, first recorded 1813. Sense of "a writing tablet" (made of slate), first recorded late 14c., led to that of "list of preliminary candidates prepared by party managers," first recorded 1842, from notion of being easily altered or erased. Clean slate (1856) is an image from customer accounts chalked up in a tavern.
slate (v.): 1520s, "to cover with slates" (earlier sclatten, late 15c.), from slate (n.). Meaning "propose, schedule" is from 1883; earlier "to nominate" (1804); the notion is of writing on a slate board. Related: Slated; slating.
slater (n.): "one who makes or lays slates," c. 1400 (mid-13c. as a surname), agent noun from slate.
slather (v.): "spread liberally," 1847, of uncertain origin. Early 19c. local glossaries from western England have the word with a sense "to slip or slide."
Slather on the manure on all the hoed crops, if you have it; if not buy of your improvident neighbor. ["Genesee Farmer," June 1847]
Sometimes said to be from a dialectal noun meaning "large amount" (usually as plural, slathers), but this is first attested 1855. Related: Slathered; slathering.
slattern (n.): 1630s, "a woman negligent or disordered in her dress or household," of uncertain origin, probably related to Low German Slattje, Dutch slodder, dialectal Swedish slata "slut" (in the older, non-sexual sense; compare slut). Compare dialectal English verb slatter "to spill or splash awkwardly, to waste," used of women or girls considered untidy or slovenly.
slatternly (adj.): 1670s, from slattern + -ly (1).
slaughter (n.): c. 1300, "killing of a cattle or sheep for food, killing of a person," from a Scandinavian *slahtr, akin to Old Norse slatr "a butchering, butcher meat," slatra "to slaughter," slattr "a mowing" from Proto-Germanic *slukhtis, related to Old Norse sla "to strike" (see slay (v.)) + formative suffix (as in laugh/laughter). Meaning "killing of a large number of persons in battle" is attested from mid-14c. Old English had slieht "stroke, slaughter, murder, death; animals for slaughter;" as in sliehtswyn "pig for killing."
slaughter (v.): 1530s, "butcher an animal for market," from slaughter (n.). Meaning "slay wantonly, ruthlessly, or in great numbers" is from 1580s. Related: Slaughtered; slaughtering.
slaughterhouse (n.): also slaughter-house, late 14c., "place where animals are butchered for market," from slaughter (n.) + house (n.). The Slaughter-house cases in U.S. history were 1873.
Slav (n.): late 14c., Sclave, from Medieval Latin Sclavus (c.800), from Byzantine Greek Sklabos (c.580), from Old Church Slavonic Sloveninu "a Slav," probably related to slovo "word, speech," which suggests the name originally identified a member of a speech community (compare Old Church Slavonic Nemici "Germans," related to nemu "dumb;" Greek heterophonos "foreign," literally "of different voice;" and Old English þeode, which meant both "race" and "language").

Identical with the -slav in personal names (such as Russian Miroslav, literally "peaceful fame;" Mstislav "vengeful fame;" Jaroslav "famed for fury;" Czech Bohuslav "God's glory;" and see Wenceslas). Spelled Slave c. 1788-1866, influenced by French and German Slave. As an adjective from 1876.
Slave: Indian tribe of northwestern Canada, 1789, from slave (n.), translating Cree (Algonquian) awahkan "captive, slave."
slave (v.): 1550s, "to enslave," from slave (n.). The meaning "work like a slave" is first recorded 1719. Related: Slaved; slaving.
slave (n.): late 13c., "person who is the chattel or property of another," from Old French esclave (13c.), from Medieval Latin Sclavus "slave" (source also of Italian schiavo, French esclave, Spanish esclavo), originally "Slav" (see Slav); so used in this secondary sense because of the many Slavs sold into slavery by conquering peoples.
This sense development arose in the consequence of the wars waged by Otto the Great and his successors against the Slavs, a great number of whom they took captive and sold into slavery. [Klein]
Meaning "one who has lost the power of resistance to some habit or vice" is from 1550s. Applied to devices from 1904, especially those which are controlled by others (compare slave jib in sailing, similarly of locomotives, flash bulbs, amplifiers). Slave-driver is attested from 1807; extended sense of "cruel or exacting task-master" is by 1854. Slave state in U.S. history is from 1812. Slave-trade is attested from 1734.

Old English Wealh "Briton" also began to be used in the sense of "serf, slave" c.850; and Sanskrit dasa-, which can mean "slave," apparently is connected to dasyu- "pre-Aryan inhabitant of India." Grose's dictionary (1785) has under Negroe "A black-a-moor; figuratively used for a slave," without regard to race. More common Old English words for slave were þeow (related to þeowian "to serve") and þræl (see thrall). The Slavic words for "slave" (Russian rab, Serbo-Croatian rob, Old Church Slavonic rabu) are from Old Slavic *orbu, from the PIE root *orbh- (also source of orphan), the ground sense of which seems to be "thing that changes allegiance" (in the case of the slave, from himself to his master). The Slavic word is also the source of robot.
slaver (v.): "dribble from the mouth," early 14c., from Old Norse slafra "to slaver," probably imitative (compare slobber (v.)). Related: Slavered; slavering. The noun is from early 14c.
slaver (n.): "ship in the slave trade," 1830, agent noun from slave (v.). Meaning "person in the slave trade" is from 1842.
slavery (n.): 1550s, "severe toil, hard work, drudgery;" from slave (v.) + -ery. Meaning "state of servitude" is from 1570s; meaning "keeping or holding of slaves" is from 1728.
Slavic (adj.): 1813; see Slav + -ic. Earlier in same sense was Slavonic (1640s), from Slavonia, a region of Croatia; Slavonian (1570s). As a noun in reference to a language group from 1812.
slavish (adj.): 1560s, from slave (n.) + -ish. Sense of "servilely imitative, lacking originality or independence" is from 1753. Related: Slavishly; slavishness.
slavocracy (n.): also slaveocracy, in U.S. history, "the political dominance of slave-owners," 1840, formed irregularly from slave (n.) + -cracy. Related: Slavocrat.
slaw (n.): "sliced cabbage," 1794, from Dutch sla, short for salade, from French salade (see salad).