Online Etymology Dictionary

sitz-bath (n.): 1849, a hybrid, from German Sitzbad, literally "bath in a sitting position," with English bath for German Bad.
sitzkrieg (n.): 1940, "static warfare" (such as prevailed in Europe in the winter of 1939-40), R.A.F. coinage on analogy of blitzkrieg (q.v.), from German sitz "a sitting."
Siva (n.): one of the three supreme gods of Hinduism, lord of destruction and reproduction, 1788, from Hindi Shiva, from Sanskrit Sivah, literally "propitious, gracious," from PIE *ki-wo-, from root *kei- "beloved, dear" (connected with Latin civis "citizen," literally "member of a household"), also "to lie, couch" (cf. cemetery).
six (n.): Old English siex, from Proto-Germanic *sekhs (cf. Old Saxon seks, Old Norse and Old Frisian sex, Middle Dutch sesse, Dutch zes, Old High German sehs, German sechs, Gothic saihs), from PIE *seks (cf. Sanskrit sas, Avestan kshvash, Greek hex, Latin sex, Old Church Slavonic sesti, Lithuanian sesi, Old Irish se, Welsh chwech).

Six-shooter is first attested 1844; six-pack of beverage is from 1952. Six of one and half-a-dozen of the other "little difference" is recorded from 1836. Phrase at sixes and sevens "hazarding all ones chances," is first in Chaucer, perhaps from dicing (the original form was on six and seven) and could be a corruption of on cinque and sice, using the French names (which were common in Middle English) for the highest numbers on the dice.
sixpence (n.): late 14c., "sum of six pennies," from six + pence. As a specific British coin, from 1590s.
sixteen: Old English sixtyne, from siex (see six) + -teen. Cf. Old Frisian sextine, Middle Dutch sestien, Old Norse sextan.
The age of the gods is always sixteen. Sixteen represents the number of perfection, of plenitude. In man it is after the sixteenth year that the first elements of decay begin to appear, and when the moon reaches the sixteenth digit it begins to decrease. [Alain Daniélou, "The Myths and Gods of India"]
sixth: Old English syxte, from siex (see six). Sixth sense "supernatural perception of objects" is attested from 1807; earlier it meant "the sense that apprehends sexual pleasure" (1690s).
sixties (n.): 1848 as the years of someone's life between 60 and 69; 1827 as a decade of years in a given century. See sixty.
sixty: Old English sixtig, from siex (see six) + -tig (see -ty (1)). Phrase sixty-four dollar question is 1942, from radio quiz show where that was the top prize. Sixty-nine in sexual sense is first attested 1888, as a translation of French faire soixante neuf, literally "to do 69."
size (n.): c.1300, "an ordinance to fix the amount of a payment or tax," from Old French sise, shortened form of assise "session, assessment, regulation, manner" (see assize), probably a misdivision of l'assise as la sise. The sense of "extent, amount, magnitude" (c.1400) is from the notion of regulating something by fixing the amount of it (weights, food portions, etc.). Specific sense of "set of dimensions of an article of clothing or shoe" is attested from 1590s.
size (v.): c.1400, "to regulate," from size (n.). Meaning "to make of a certain size" is from c.1600; that of "to classify according to size" is first attested 1630s. Verbal phrase size up "estimate, assess" is from 1847 and retains the root sense of size (n.).
sizeable (adj.): also sizable, 1610s, from size + -able. Related: Sizeably; sizeableness.
sizer (n.): 1670s, agent noun from size.
sizzle (v.): c.1600, perhaps a frequentative form of Middle English sissen "hiss, buzz," of imitative origin. The figurative sense is attested from 1859. Related: Sizzled; sizzling. The noun is first recorded 1823.
ska (n.): 1964, Jamaican, of unknown origin.
skag (n.): "heroin," 1967, American English, earlier "cigarette" (1915), of unknown origin.
skald (n.): 1763, "Scandinavian poet and singer of medieval times," from Old Norse skald "skald, poet" (9c.), of unknown origin, perhaps from PIE root *sekw- "to say, utter." The modern word is an antiquarian revival. "Usually applied to Norwegian and Icelandic poets of the Viking period and down to c 1250, but often without any clear idea as to their function and the character of their work." [OED]
skank (n.): "unattractive woman," 1965, perhaps from skag in this sense (1920s), of unknown origin. Meaning "dance to reggae music" is 1976, probably not the same word, but also of unknown origin.
skanky (adj.): "ugly, unattractive" (originally of women), by 1965, U.S. Black slang; see skank.
skat (n.): "card game," 1864, from German skat, from Italian scarto "rejection of a card," cognate with French écarté "card."
skate (n.1): type of flat, cartilaginous fish, mid-14c., from Old Norse skata, of unknown origin.
skate (n.2): "ice skate or roller skate," 1660s, skeates "ice skates" (the custom was brought to England after the Restoration by exiled followers of Charles II who had taken refuge in Holland), from Dutch schaats (singular, mistaken in English as plural), from Middle Dutch schaetse, from Old North French escache "a stilt, trestle," from Old French eschace "stilt" (French échasse), from Frankish *skakkja "stilt" (cf. Frisian skatja "stilt"), perhaps literally "thing that shakes or moves fast" and related to root of Old English sceacan "to vibrate" (see shake). Or perhaps the Dutch word is connected to Middle Low German schenke, Old English scanca "leg" (see shank). Sense alteration in Dutch from "stilt" to "skate" is not clearly traced.
skate (v.): 1690s, from skate (n.2). U.S. slang sense of "to get away with something" is attested from 1945. Related: Skated; skating.
skateboard: 1964, noun and verb, from skate (v.) on model of surfboard. The phenomenon began c.1963 in southern California and was nationwide the following summer.
Skateboarding requires only a tapered piece of wood flexibly mounted on roller-skate wheels and a stretch of pavement -- preferably downhill and away from traffic. ["Life," June 5, 1964]
skedaddle (v.): "to run away," 1861, American Civil War military slang, of unknown origin, perhaps connected to earlier use in northern England dialect with a meaning "to spill." Liberman says it "has no connection with any word of Greek, Irish, or Swedish, and it is not a blend." He calls it instead an "enlargement of dial. scaddle 'scare, frighten.'"
Skee-Ball (n.): 1909, proprietary name, U.S.
skeet (n.): form of trapshooting, 1926, a name chosen as "a very old form of our present word 'shoot.' " Perhaps Old Norse skotja "to shoot" (see shoot) was intended.
skein (n.): mid-15c., from Middle French escaigne "a hank of yarn," from Old French escagne (mid-14c.), of uncertain origin.
skeletal (adj.): 1854; see skeleton + -al (1).
skeleton (n.): 1570s, from Modern Latin sceleton "bones, bony framework of the body," from Greek skeleton soma "dried-up body, mummy," from neuter of skeletos "dried-up," from skellein "dry up," from PIE root *skele- "to parch, whither" (cf. Greek skleros "hard"). The Greek word was borrowed in Late Latin (sceletus), hence French squelette, Spanish esqueleto, Italian scheletro. The meaning "bare outline" is first recorded c.1600; hence skeleton crew (1778), skeleton key, etc. Phrase skeleton in the closet "source of secret shame to a person or family" popularized 1845 by Thackeray, though he likely didn't coin it.
skene (n.): Celtic dagger, 1520s, from Irish Gaelic scian (genitive sceine) "knife."
skep (n.): c.1100, from Old Norse skeppa "basket, bushel."
skeptic (n.): also sceptic, 1580s, "member of an ancient Greek school that doubted the possibility of real knowledge," from French sceptique, from Latin scepticus, from Greek skeptikos (plural Skeptikoi "the Skeptics"), literally "inquiring, reflective," the name taken by the disciples of the Greek philosopher Pyrrho (c.360-c.270 B.C.E.), from skeptesthai "to reflect, look, view" (see scope (n.1)). The extended sense of "one with a doubting attitude" first recorded 1610s. The sk- spelling is an early 17c. Greek revival and is preferred in U.S.
Skeptic does not mean him who doubts, but him who investigates or researches as opposed to him who asserts and thinks that he has found. [Miguel de Unamuno, "Essays and Soliloquies," 1924]
skeptical (adj.): also sceptical; see skeptic + -al (1). Related: Skeptically.
skepticism (n.): also scepticism, 1640s, from skeptic + -ism. Specifically regarding Christian religion, from 1800.
sketch (n.): "rough drawing intended to serve as the bases for a finished picture," 1660s, from Dutch schets, from Italian schizzo "sketch, drawing," literally "a splash, squirt," from schizzare "to splash or squirt," of uncertain origin, perhaps from Latin schedium "an extemporaneous poem," from Greek skedios "temporary, extemporaneous," related to skhein, aor. inf. of ekhein "to have" (see scheme). German Skizze, French esquisse, Spanish esquicio are from Italian. Extended sense of "brief account" is from 1660s; meaning "short play or performance, usually comic" is from 1789.
sketch (v.): 1690s, from sketch (n.). Related: Sketched; sketcher; sketching.
sketchy (adj.): 1805, from sketch (n.) + -y (1). Colloquial sense of "unsubstantial, imperfect, flimsy" is from 1878. Related: Sketchiness.
skew (v.): late 15c., from Old North French eskiuer "shy away from, avoid," Old French eschiver (see eschew). Meaning "depict unfairly" first recorded 1872, on notion of being slanted. Statistical sense dates from 1929. Related: Skewed; skewing. The adjectival meaning "slanting, turned to one side" is recorded from c.1600; noun meaning "slant, deviation" first attested 1680s.
skewbald: "horse with brown and white patches," 1650s, from skued "skewbald" (mid-15c.), of unknown origin, + bald "having white patches" (see bald). First element apparently unconnected with skew (v.); OED suggests perhaps from Old French escu "shield," but also notes a close resemblance in form and sense with Icelandic skjottr, "the history of which is equally obscure."
When the white is mixed with black it is called 'pie-bald,' with bay the name of 'skew-bald' is given to it. ["Youatt's 'The Horse,' " 1866]
skewer (n.): 1670s, variant of skiver (1660s), perhaps from Old Norse skifa "disk, cut, slice," related to shiver (n.). The verb is attested from 1701, from the noun. Related: Skewered; skewering.
skewness (n.): 1894, from skew + -ness.
ski (n.): 1885 (there is an isolated instance from 1755), from Norwegian ski, related to Old Norse skið "snowshoe," literally "stick of wood," cognate with Old English scid "stick of wood," obsolete English shide; Old High German skit, German Scheit "log," from Proto-Germanic *skid- "to divide, split," from PIE root *skei- "to cut, split" (see shed (v.)). The verb is 1893, from the noun. ski-jumper is from 1894; ski bum first attested 1960.
skid (n.): c.1600, "beam or plank on which something rests," probably from a Scandinavian source akin to Old Norse skið "stick of wood" (see ski). A skid as something used to facilitate downhill motion (cf. skid row) led to figurative phrases such as hit the skids "go into rapid decline" (1920).
skid (v.): 1670s, "apply a skid to (a wheel, to keep it from turning)," from skid (n.). Meaning "slide along" first recorded 1838; extended sense of "slip sideways" (on a wet road, etc.) first recorded 1884 (the noun in this sense is attested from 1907). The original notion is of a block of wood for stopping a wheel; the modern senses are from the notion of a wheel slipping when blocked from revolving.
skid row (n.): 1931, from skid road "track of skids along which logs are rolled" (1851), from skid (n.). The sense was extended to "part of town inhabited by loggers" (1906), then, by hobos, to "disreputable district" (1915).
skidoo (v.): 1905, "to leave in a hurry," perhaps a variant of skedaddle (q.v.). Sense in early 20c. slang phrase twenty-three skidoo (1906) is obscure.
skier (n.): 1895, agent noun from ski (v.).
skiff (n.): "small boat," 1570s, from French esquif (1540s), from Italian schifo "little boat," from a Germanic source (e.g. Old High German scif "boat;" see ship (n.)). Originally the small boat of a ship.
skiffle (n.): style of U.K. pop music, 1957, from U.S. slang meaning "type of jazz played on improvised instruments" (1926), of unknown origin.