Online Etymology Dictionary

site (v.): "to give a location to, place," 1590s, from site (n.). Related: Sited; siting.
sith (adv., conj., prep.): "since" (obsolete), Middle English, reduced from Old English siððan "then, thereupon; continuously, during which; seeing that," from *sið þon "subsequent to that," from sið "after," from Proto-Germanic *sith- "later, after" (source also of Old Saxon sith "after that, since, later," German seit "since," Gothic seiþus "late"), from PIE *se- (2) "long, late" (see soiree).
sitophobia (n.): "morbid aversion to food" (or certain foods), 1882, from Greek sitos "wheat, corn, meal; food," of unknown origin, + -phobia. Related: Sitophobe; sitophobic.
sitter (n.): c. 1300, "one that sits," agent noun from sit (v.). As short for baby-sitter from 1937.
sitting (n.): early 13c., verbal noun from sit (v.). Meaning "a meeting of a body" is from c. 1400. Meaning "interval during which one sits" (for some purpose, especially to have one's portrait taken) is from 1706. Sitting-room first recorded 1771. Slang sitting duck "easy target" first recorded 1944; literal sense is from 1867 (it is considered not sporting to shoot at one).
situ: see in situ.
situate (v.): early 15c., "to place in a particular state or condition," from Medieval Latin situatus, past participle of situare "to place, locate," from Latin situs "a place, position" (see site). Related: Situated; situating.
situate (adj.): 1520s, now obsolete, adjective from Late Latin situatus, past participle of situare (see situate (v.)).
situation (n.): early 15c., "place, position, or location," from Middle French situation or directly from Medieval Latin situationem (nominative situatio) "a position, situation," noun of action from past participle stem of situare "to place, locate" (see situate). Meaning "state of affairs" is from 1710; meaning "employment post" is from 1803.
situational (adj.): 1903, from situation + -al. Related: Situationally. Situational ethics attested from 1969 (situation ethics first attested 1955).
situs (n.): Latin, "situation, position" (see site). In technical uses in English, "proper or original position and location of something" (as in in situ).
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.): also Shiva, 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" (compare cemetery). But by some this is said to be a euphemism. Related: Sivaism; Sivaistic.
six (n.): Old English siex, six, sex, from Proto-Germanic *sekhs (source also of Old Saxon and Danish seks, Old Norse, Swedish, and Old Frisian sex, Middle Dutch sesse, Dutch zes, Old High German sehs, German sechs, Gothic saihs), from PIE *s(w)eks (source also of Sanskrit sas, Avestan kshvash, Persian shash, Greek hex, Latin sex, Old Church Slavonic sesti, Polish sześć, Russian shesti, Lithuanian szeszi, Old Irish se, Welsh chwech).

Six-shooter, usually a revolver with six chambers, is first attested 1844; six-pack of beverage containers is from 1952, of abdominal muscles by 1995. Six of one and half-a-dozen of the other "little difference" is recorded from 1833. Six-figure in reference to hundreds of thousands (of dollars, etc.) is from 1840. Six feet under "dead" is from 1942.

Phrase at sixes and sevens originally was "hazarding all one's chances," first in Chaucer, perhaps from dicing (the original form was on six and seven); it 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. Meaning "at odds, in disagreement or confusion" is from 1785, perhaps via a notion of "left unsettled."
sixfold (adj.): Old English sixfeald; see six + -fold. Similar formation in Danish sexfold, Dutch zes-voudig; German sechsfältig, Swedish sexfaldig.
sixpence (n.): late 14c., "sum of six pennies," from six + pence. As a specific British coin, from 1590s. Sixpenny (adj.) had a figurative sense "paltry, cheap, petty, worthless" by 1560s; sixpenny nails (early 15c.) cost so much per hundred.
sixteen: Old English sixtyne, from siex (see six) + -teen. Similar formation in Old Frisian sextine, Middle Dutch sestien, Dutch zestien, German sechzehn, 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"]
From Latin contracted form sexdecim, sedecim come Italian sedici, French seize.
sixteenmo (n.): "book printed on sheets of 16 leaves," 1847, from an English reading of the printers' Latin abbreviation 16-mo, representing sexto decimo "sixteen."
sixteenth (adj.): early 13c., from sixteen + -th (1); replacing sixtethe, sixteothe, forms based on Old English syxteoða. Cf Old Frisian sextinda, Middle Dutch sestiende, German sechzehnte, Old Norse sextandi. Musical sixteenth note is from 1861.
sixth (adj.): 1520s, replacing Middle English sixte (c. 1200), from Old English syxte, from siex (see six). Compare Old Frisian sexta, Middle Dutch seste, Old High German sehsto, German sechste, Gothic saihsta. With ending conformed to -th (1). Related: Sixthly. The noun meaning "a sixth part" is from 1550s. As a music tone, from 1590s. Sixth sense "supernatural perception of objects" is attested from 1712; earlier it meant "titillation, the sense that apprehends sexual pleasure" (1690s, from Scaliger).
Then said Peter, That is false; for there is a sixth Sense, that of Prescience : for the other five Senses are capable only of Knowledg ; but the Sixth of Foreknowledg ; which Sense the Prophets had. [William Whitson, "Primitive Christianity Reviv'd," vol. V, London, 1712]
sixties (n.): 1848 as the years of someone's life between 60 and 69; 1827 as the seventh decade of years in a given century. See sixty.
sixtieth: Old English sixteogoða "sixtieth;" see sixty + -th (1).
sixty: Old English sixtig, from siex (see six) + -tig (see -ty (1)). Similar formation in Old Norse sextugr, sextögr, sextigir, Old Frisian sextich, Middle Dutch sestig, Dutch zestig, Old High German sehszug, German sechzig. Phrase sixty-four dollar question is 1942, from radio quiz show where that was the top prize.
sixty-nine (n.): in sexual sense, 1888, as a translation of French faire soixante neuf, literally "to do 69." So called from the similarity of positions to the arrangement of the numerals.
sixtyfold: also sixty-fold, Old English sixtigfeald; see sixty + -fold.
sizar (n.): also sizer, at certain British universities, a student of limited means who received school meals for free, 1580s, from size (n.) in a specialized sense "ration, allowance for provisions."
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.). Related: Sized; sizing.
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, volume, magnitude" (c. 1300) is from the notion of regulating something by fixing the amount of it (weights, food portions, etc.). Specific sense of "set of dimensions of a manufactured article for sale" is attested from 1590s.
sizeable (adj.): also sizable, 1610s, "of relatively good, suitable, or desirable size, usually somewhat large" [Century Dictionary], from size + -able. Related: Sizeably; sizeableness.
sizer (n.): "device for measuring sizes," 1670s, agent noun from size (v.).
sizzle (v.): c. 1600, "to burn with a hissing sound," perhaps a frequentative form of Middle English sissen "hiss, buzz" (c. 1300), 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.): "Scandinavian poet and singer of medieval times," 1763, from Old Norse skald "skald, poet" (9c.), of unknown origin, perhaps from PIE root *sekw- (3) "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]. Related: Scaldic.
skank (n.): "unattractive woman," 1965, perhaps from skag in this sense (1920s), which is of unknown origin. Verbal meaning "dance to reggae music" is from 1976, probably not the same word but also of unknown origin. Related: Skanking.
skanky (adj.): "ugly, unattractive" (originally of women), by 1965, African-American vernacular; see skank.
skat (n.): card game, 1864, from German Skat (by 1838), from earlier scart (said to have been a term used in the old card game called taroc, which was of Italian origin), from Italian scarto "cards laid aside," which is said to be a back-formation from scartare, from Latin ex- "off, away" + Late Latin carta (see card (n.1)). The German game is perhaps so called because it is played with a rump deck, or because two cards are laid aside at the start of the game, or because discarding is an important part of the game. Compare French card game écarté, literally "cards removed."
skate (n.1): "type of flat, cartilaginous fish, a kind of ray," mid-14c., from a Scandinavian source such as Old Norse skata "skate," Danish skade, Faeroese skøta, of unknown origin.
skate (n.2): "ice skate," 1660s, skeates "ice skates," from Dutch schaats (plural schaatsen), a singular mistaken in English for plural, from Middle Dutch schaetse. The word and the custom were brought to England after the Restoration by exiled followers of Charles II who had taken refuge in Holland.

The Dutch word is from Old North French escache "a stilt, trestle," related to Old French eschace "stilt" (French échasse), from Frankish *skakkja "stilt" or a similar Germanic source (compare Frisian skatja "stilt"), perhaps literally "thing that shakes or moves fast" and related to root of Old English sceacan "to vibrate" (see shake (v.)). Or perhaps [Klein] 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. Sense in English extended to roller-skates by 1876. Meaning "an act of skating" is from 1853.
skate (v.): 1690s, "to ice-skate," from skate (n.2). U.S. slang sense of "to get away with something" is attested from 1945. Related: Skated; skating. A modern Latinate word for an ice-skating rink is glaciarium (1876).
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]
skater (n.): 1700, "one who ice-skates," agent noun from skate (v.). Extended to skateboarders by 1977.
sked (n.): short for schedule, student slang from 1929.
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" [contra De Vere]. He calls it instead an "enlargement of dial. scaddle 'scare, frighten.'" Related: Skedaddled; skedaddling. As a noun from 1870.
Skee-Ball (n.): 1909, proprietary name (Skee-Ball Alley Company, Philadelphia, Pa., U.S.), the first element said to represent the old alternative spelling of ski (v.).
Skee ball bowling, in which the ball is jumped or skeed into the pockets in the same manner as a skee-jumper rises from the bump in his flight, is a new and unique hand-ball game that seems destined to great popularity. ["Popular Mechanics," July 1909]
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 (v.)) was intended.
skeeter (n.): colloquial shortening of mosquito, 1839, American English.
skeezicks (n.): 1850, "rascal, rogue," of unknown origin, perhaps a fanciful formation. In early 20c. used affectionately or playfully of children.
skein (n.): "fixed quantity of yarn doubled over and over and knotted, mid-15c., from Middle French escaigne "a hank of yarn" (Old French escagne, mid-14c., Modern French écagne), of uncertain origin. Compare Medieval Latin scagna "a skein," Irish sgainne "a skein, clue."