Online Etymology Dictionary

sleaze (n.): "condition of squalor," by 1967, back-formation from sleazy. Meaning "person of low moral standards," and the adjective use, are attested from 1976.
sleazy (adj.): 1640s, "hairy, fuzzy," later "flimsy, unsubstantial" (1660s), of unknown origin; one theory traces it somehow to Silesian "of the eastern German province of Silesia" (German Schlesien), where fine linen or cotton fabric was made (Silesia in reference to cloth is attested in English from 1670s; and sleazy as an abbreviated form is attested from 1670), but OED is against this. Sense of "sordid" is from 1941.
sled (n.): late 14c., "a sledge used for transport of heavy goods," from Middle Dutch sledde "sled," from Proto-Germanic *slido (cf. Old Saxon slido, Old Norse sleði, Danish slæde, Swedish släde, Old High German slito, German Schlitten "sledge"), from the same root as Old English slidan (see slide (v.)). In reference to a sledge used for travel or recreation, it is attested from 1580s, now mainly American English.
sled (v.): "ride on a sled," 1780, from sled (n.). Related: Sledded; sledding.
sledge (n.1): "heavy hammer," Old English slecg, from Proto-Germanic *slagj- (cf. Old Norse sleggja, Middle Swedish sleggia "sledgehammer"), related to slean "to strike" (see slay). Sledgehammer thus is pleonastic.
sledge (n.2): "sleigh," 1610s, from dialectal Dutch sleedse, variant of slede (see sled (n.)); said to be of Frisian origin.
sledgehammer (n.): late 15c., from sledge (n.1) + hammer (n.). As a verb, from 1834.
sleek (adj.): 1580s, variant of Middle English slike (see slick). Originally of healthy-looking animal hair; applied to persons 1630s, with sense of "plump and smooth-skinned."
sleep (v.): Old English slæpan "to sleep" (class VII strong verb; past tense slep, past participle slæpen), from West Germanic *slæpanan (cf. Old Saxon slapan, Old Frisian slepa, Middle Dutch slapen, Dutch slapen, Old High German slafen, German schlafen, Gothic slepan "to sleep"), from PIE root *sleb- "to be weak, sleep" (cf. Old Church Slavonic slabu, Lithuanian silpnas "weak"), which is perhaps connected to the root of slack (adj.). Sleep with "do the sex act with" is in Old English.
Gif hwa fæmnan beswice unbeweddode, and hire mid slæpe ... [Laws of King Alfred, c.900]
Sleep around first attested 1928. Sleeping sickness as a specific African tropical disease is first recorded 1875.
sleep (n.): Old English slæp from the root of sleep (v.); cf. cognate Old Saxon slap, Old Frisian slep, Middle Dutch slæp, Dutch slaap, Old High German slaf, German Schlaf, Gothic sleps.

Personified in Latin as Somnus, in Greek as Hypnos (see somnolence). Figurative use for "repose of death" was in Old English; to put (an animal) to sleep "kill painlessly" is recorded from 1923 (a similar imagery underlies cemetery). Sleep deprivation attested from 1906. Sleep-walker "somnambulist" is attested from 1747. To be able to do something in (one's) sleep "easily" is recorded from 1953.
sleeper (n.): early 13c., "one who sleeps, one who is inclined to sleep much," agent noun of sleep (v.). Meaning "railroad sleeping car" is from 1875. Sense of "something whose importance proves to be greater than expected" first attested 1892, originally in American English. sports jargon, probably from earlier gambling slang (1856) sense of "unexpected winning card." Meaning "spy, enemy agent, etc. who remains undercover for a long time before attempting his purpose" first attested 1955, originally in reference to communist agents in the West.
sleepless (adj.): early 15c., from sleep (n.) + -less. Related: Sleeplessly; sleeplessness.
sleepy (adj.): early 13c., from sleep (n.) + -y (2). Related: Sleepily; sleepiness.
sleet (n.): c.1300, slete, either from an unrecorded Old English word or via Middle High German sloz, Middle Low German sloten (plural) "hail," from Proto-Germanic *slautjan- (cf. dialectal Norwegian slutr, Danish slud, Swedish sloud "sleet"), from root *slaut-.
sleet (v.): early 14c., from sleet (n.). Related: Sleeted; sleeting.
sleeve (n.): Old English sliefe (West Saxon), slefe (Mercian), from Proto-Germanic *slaubjon (cf. Middle Low German sloven "to dress carelessly," Old High German sloufen "to put on or off"). Related to Old English sliefan "put on (clothes)" and slupan "to slip, glide," from PIE root *sleubh- "to slide, slip." (cf. expression to slip into "to dress in"). Mechanical sense is attested from 1864. To have something up one's sleeve is recorded from c.1500. Meaning "the English Channel" translates French La Manche.
sleigh (n.): 1703, American and Canadian English, from Dutch slee, shortened from slede (see sled). Sleigh-ride is first recorded 1770; sleigh-bells is from c.1780.
sleight (n.): "cunning," late 13c., from Old Norse sloegð "cleverness, cunning, slyness," from sloegr (see sly). Term sleight of hand is attested from c.1400.
slender (adj.): c.1300, probably from a French source, often said to be from Old French esclendre "thin, slender," which could be from Old Dutch slinder, but the connections, and even the existence of these words, is doubtful.
slenderize: 1921, from slender + -ize. Related: Slenderized; slenderizing.
sleuth (n.): c.1200, "track or trail of a person," from Old Norse sloð "trail," of uncertain origin. Meaning "detective" is 1872, shortening of sleuthhound "keen investigator" (1849), a figurative use of a word for a kind of bloodhound that dates back to late 14c. The verb (intransitive) meaning "to act as a detective, investigate" is recorded from 1912. Related: Sleuthed; sleuthing.
slew (n.1): "swampy place," 1708, North American variant of slough.
slew (v.): "to turn, swing, twist," 1834, earlier slue (1769), a nautical word, of unknown origin. Slewed (1801) is old nautical slang for "drunk."
slew (n.2): "large number," 1839, from Irish sluagh "a host, crowd, multitude."
slice (n.): c.1300, "a fragment," from Old French esclis "splinter," a back-formation from esclicier "to splinter," from Frankish *slitan "to split" or some other Germanic source (cf. Old High German slizan; see slit). Meaning "piece cut from something" emerged early 15c. Meaning "a slicing stroke" (in golf, tennis) is recorded from 1886. Slice of life (1895) translates French tranche de la vie, a term from French Naturalist literature.
slice (v.): early 15c., from Middle French esclicier (see slice (n.)). Related: Sliced; slicing. Sliced bread introduced 1958; greatest thing since ... first attested 1969.
No matter how thick or how thin you slice it it's still baloney. [Carl Sandburg, "The People, Yes," 1936]
slick (v.): Old English -slician (attested in nigslicod "newly made sleek"), from Proto-Germanic *slikojanan, from base *slikaz (cf. Old Norse slikr "smooth," Old High German slihhan, German schleichen "to creep, crawl, sneak," Dutch slijk "mud, mire"), from PIE *sleig- "to smooth, glide, be muddy," from root *(s)lei- "slimy" (see slime (n.)). The adjective is first attested c.1300, "smooth, glossy, sleek" (of skin or hair); sense of "clever in deception" is first recorded 1590s.
slick (n.): 1620s, a kind of cosmetic, from slick (v.). Meaning "smooth place on the surface of water caused by oil, etc." is attested from 1849. Meaning "a swindler, clever person" is attested from 1959.
slicker (n.): "waterproof raincoat," 1884, from slick (v.); sense of "clever and crafty person" is from 1900.
slide (v.): Old English slidan "move smoothly, glide," from Proto-Germanic *slidanan (cf. Old High German slito, German Schlitten "sledge"), from PIE root *(s)lei- "slide" (cf. Lithuanian slystu "to glide, slide," Old Church Slavonic sledu "track," Greek olisthos "slipperiness," olisthanein "to slip," Middle Irish sloet "slide"). Phrase to let (something) slide is recorded from late 14c. The noun is 1560s, from the verb. Meaning "picture prepared for use with a projector" is attested from 1819 (in magic lantern shows). Slider as a type of baseball pitch is recorded from 1936.
slide-rule (n.): also slide rule, calculating tool, 1838, from slide (v.) + rule (n.). So called for its method of operation.
slight (adj.): early 14c., "flat, smooth; hairless," from a Scandinavian source akin to Old Norse slettr "smooth, sleek," from Proto-Germanic *slikhtaz (cf. Old Saxon slicht; Low German slicht "smooth, plain common;" Old English -sliht "level," attested in eorðslihtes "level with the ground;" Old Frisian sliucht, Middle Dutch sleht, Old High German sleht, Gothic slaihts "smooth"), probably from a collateral form of PIE root *sleig- "to smooth, glide."

Sense evolution is from "smooth" (c.1300), to "trifling, inferior" (early 14c.), to "slender, weak; of poor quality, flimsy" (late 14c.). Sense of German cognate schlecht developed from "smooth, plain, simple" to "bad," and as it did it was replaced in the original senses by schlicht, a back-formation from schlichten "to smooth, to plane," a derivative of schlecht in the old sense.
slight (v.): "treat with indifference," 1590s, from slight (adj.) in sense of "having little worth." Related: Slighted; slighting.
slim (adj.): 1650s, "thin, slight, slender," from Dutch slim "bad, sly, clever," from Middle Dutch slim "bad, crooked," from Proto-Germanic *slembaz "oblique, crooked" (cf. Middle High German slimp "slanting, awry," German schlimm "bad"). Slimnastics first recorded 1967 (with an isolated use from 1959). Slim Jim attested from 1887 in sense of "very thin person;" from 1902 as a type of slender cigar; from 1975 as a brand of meat snack.
slim (v.): "try to reduce (one's) weight," 1930, from slim (adj.). Related: Slimmed; slimming.
slime (n.): Old English slim "slime," from Proto-Germanic *slimaz (cf. Old Norse slim, Old Frisian slym, Dutch slijm, German Schleim "slime"), probably related to Old English lim "birdlime; sticky substance," from PIE root *(s)lei- "slime, slimy, sticky, slippery" (cf. Sanskrit linati "sticks, stays, adheres to; slips into, disappears;" Russian slimak "snail;" Old Church Slavonic slina "spittle;" Old Irish sligim "to smear," leinam "I follow," literally "I stick to;" Welsh llyfn "smooth;" Greek leimax "snail," limne "marsh, pool, lake," alinein "to anoint, besmear;" Latin limus "slime, mud, mire," linere "to daub, besmear, rub out, erase").
slime (v.): "to cover with slime," 1620s, from slime (n.). Related: Slimed; sliming.
slimming (adj.): "producing an appearance of thinness," 1925, present participle adjective from slim (v.).
slimy (adj.): late 14c.,from slime (n.) + -y (2). Cf. Middle Dutch slimich, Dutch slijmig, German schleimig. Figurative sense of "morally repulsive" is first attested 1570s. Related: Sliminess.
sling (n.1): c.1300, "implement for throwing stones," from an unidentified continental source, e.g. Middle Low German slinge "sling," from Proto-Germanic *slenganan (cf. Old High German slingan, German schlingen "to swing to and fro, wind, twist;" Old English slingan "to creep, twist;" Old Frisian slinge, Old High German slinga, German Schlinge "sling;" Middle Swedish slonga "noose, knot, snare").

The notion probably is of a sling being twisted and twirled before it is thrown. Sense of "loop for lifting or carrying heavy objects" first recorded early 14c. Meaning "piece of cloth tied around the neck to support an injured arm" is first attested 1720.
sling (v.): early 13c., "to knock down," later "to throw," originally "to throw with a sling" (early 14c.), from Old Norse slyngva, from the root of sling (n.1).
sling (n.2): "sweet flavored liquor drink," 1807, American English, of unknown origin; perhaps literally "to throw back" a drink, or from German schlingen "to swallow."
slingshot (n.): 1849, from sling (v.) + shot (n.). As a verb, from 1969. The piece of stone or metal hurled from it is a slung-shot (1848).
slink (v.): Old English slincan "to creep, crawl" (of reptiles), from Proto-Germanic *slenkanan (cf. Swedish slinka "to glide," Dutch slinken "to shrink, shrivel;" related to sling (v.)). Of persons, attested from late 14c. Related: Slinked; slinking.
slinky (adj.): "sinuous and slender," of women or clothes, 1921, from slink + -y (2). As a proprietary name (with capital from S-) for a spring marketed as a toy, 1948, by James Industries Inc., Philadelphia, U.S.A.
slip (v.): c.1300, "to escape, to move softly and quickly," from Middle Low German slippen "to glide, slide," from Proto-Germanic *slipanan (cf. Old High German slifan, Middle Dutch slippen, German schleifen "to glide, slide"), from PIE *sleib- "slimy, slippery," from root *(s)lei- "slimy, sticky, slippery" (see slime (n.)). Meaning "to lose one's footing" is from mid-14c. Related: Slipped; slipping. To slip up "make a mistake" is from 1855; to slip through the net "evade detection" is from 1902.
slip (n.): "woman's sleeveless garment," 1761, from slip (v.). Meaning "mistake, minor fault" is from 1610s. To give (someone) the slip is from 1560s.
slip (n.): "narrow strip," mid-15c., probably from Middle Low German or Middle Dutch slippe "cut, slit," possibly related to Old English toslifan "to split, cleave." Sense of "sprig for planting or grafting" first recorded in late 15c.; that of "young slender person" (a slip of a girl) in 1580s; that of "narrow piece of paper" (e.g. pink slip) in 1680s. Meaning "boat ramp" is from 1769. The meaning "potter's clay" is a different word, from Old English slyppe "slime," related to slupan "to slip."
slipknot (n.): also slip-knot, 1650s, from slip (v.) + knot (n.).
slippage (n.): 1850, from slip (v.) + -age.