Online Etymology Dictionary

sinker (n.): 1838 in the fishing-line sense, agent noun from sink (v.).
sinkhole (n.): also sink-hole, mid-15c., "sewage pit," from sink (n.) + hole (n.). As a geological phenomenon, "hole made in the earth in limestone regions by underground erosion," 1780, from sink (v.).
sinless (adj.): Old English synleas; see sin (n.) + -less. Related: Sinlessly; sinlessness.
Sinn Fein (n.): 1905, from Irish, literally "we ourselves," from Old Irish féin "self," from PIE *swei-no-, suffixed form of root *s(w)e- (see idiom). Movement founded 1905 by Irish journalist and politician Arthur Griffith (1872-1922).
sinner (n.): mid-14c., agent noun from sin (v.). Old English had synngiend in this sense.
Sino-: before vowels Sin-, word-forming element meaning "Chinese," 1879, from Late Latin Sinæ (plural) "the Chinese," from Ptolemaic Greek Sinai, from Arabic Sin "China," probably from Chinese Ch'in, name of the fourth dynasty of China (see China).
Sinologist (n.): 1814; see Sino- + -logy + -ist. Related: Sinology (1834).
Sinon: name of the Greek who induced the Trojans to take the wooden horse into the city; hence "a deceiver by false tales."
Sinophobe (n.): 1919, from Sino- + phobe. Related: Sinophobic; Sinophobia (1876).
sinsemilla (n.): potent strain of marijuana, 1975, from Mexican Spanish, literally "without seed," from Latin sine "without" (see sans) + semen "seed" (see semen).
sinter (n.): 1780, from German Sinter, cognate with English cinder.
sinuate (adj.): 1680s, from Latin sinuatus, past participle of sinuare (see insinuate).
sinuous (adj.): "full of turns and curves," 1570s, from Latin sinuosus "full of curves, folds, or bendings," from sinus "curve, fold, bend" (see sinus). Related: Sinuously; sinuousness.
sinus (n.): "hollow curve or cavity in the body," early 15c., from Medieval Latin sinus, from Latin sinus "bend, fold, curve, a bent surface; a bay, bight, gulf; a fold in land;" also "fold of the toga about the breast," hence "bosom," and figuratively "love, affection, intimacy; interior, inmost part;" of unknown origin.
sinusitis (n.): "inflammation of the sinuses," 1896; see sinus + -itis "inflammation."
sinusoid: 1823 in mathematics; 1900 in physiology, from sinus + -oid. Related: Sinusoidal.
Siouan (adj.): 1885, from Sioux + -an. Replacing Dakotan.
Sioux: group of North American Indian tribes, 1761, from North American French, short for Nadouessioux, sometimes said to be from Ojibway (Algonquian) Natowessiwak (plural), literally "little snakes," from nadowe "Iroquois" (literally "big snakes"). Another explanation traces it to early Ottawa (Algonquian) singular /na:towe:ssi/ (plural /na:towe:ssiwak/) "Sioux," apparently from a verb meaning "to speak a foreign language" [Bright]. In either case, a name given by their neighbors; the people's name for themselves is Dakota.
sip (v.): late 14c., of uncertain origin, perhaps from a source related to Low German sippen "to sip," or from Old English sypian "absorb, drink in," related to supan "to take into the mouth a little at a time" (see sup (v.2)). Related: Sipped; sipping.
sip (n.): c. 1500, from sip (v.).
siphon (n.): late 14c., from Latin sipho (genitive siphonis) "a siphon," from Greek siphon "pipe, tube for drawing wine from a cask," of unknown origin. Related: Siphonal.
siphon (v.): 1859, from siphon (n.). Figurative sense of "to draw off, divert" is recorded from 1940. Related: Siphoned; siphoning.
sir: c. 1300, title of honor of a knight or baronet (until 17c. also a title of priests), variant of sire, originally used only in unstressed position. Generalized as a respectful form of address by mid-14c.; used as a salutation at the beginning of letters from early 15c.
sire (n.): c. 1200, title placed before a name and denoting knighthood, from Old French sire "lord (appellation), sire, my lord," from Vulgar Latin *seior, from Latin senior "older, elder" (see senior (adj.)). Standing alone and meaning "your majesty" it is attested from early 13c. General sense of "important elderly man" is from mid-14c.; that of "father, male parent" is from mid-13c.
sire (v.): "to beget, to be the sire of," 1610s, from sire (n.). Used chiefly of beasts, especially of stallions. Related: Sired; siring.
siren (n.): mid-14c., "sea nymph who by her singing lures sailors to their destruction," from Old French sereine (12c., Modern French sirène) and directly from Latin Siren (Late Latin Sirena), from Greek Seiren ["Odyssey," xii.39 ff.], one of the Seirenes, mythical sisters who enticed sailors to their deaths with their songs, also in Greek "a deceitful woman," perhaps literally "binder, entangler," from seira "cord, rope."

Meaning "device that makes a warning sound" (on an ambulance, etc.) first recorded 1879, in reference to steamboats, perhaps from similar use of the French word. Figurative sense of "one who sings sweetly and charms" is recorded from 1580s. The classical descriptions of them were mangled in medieval translations and glosses, resulting in odd notions of what they looked like.
Sirius (n.): brightest star by magnitude, late 14c., from Latin Sirius "the Dog Star," from Greek Seirios, said to mean literally "scorching" or "the scorcher." But other related Greek words seem to derive from this use, and the name might be a folk-etymologized borrowing from some other language. An Egyptian name for it was Sothis. The connection of the star with scorching heat is from its ancient heliacal rising at the summer solstice (see dog days). Also see dog star. Related: Sirian. The constellation Canis Major seems to have grown from the star, not the other way.
Homer made much of it as [Kyon], but his Dog doubtless was limited to the star Sirius, as among the ancients generally till, at some unknown date, the constellation was formed as we have it, -- indeed till long afterwards, for we find many allusions to the Dog in which we are uncertain whether the constellation or its lucida is referred to. [Richard Hinckley Allen, Canis Major in "Star Names and Their Meanings," London: 1899]
sirloin (n.): early 15c., surloine, from Middle French surlonge, literally "upper part of the loin," from sur "over, above" (see sur-) + longe "loin," from Old French loigne (see loin).

English spelling with sir- dates from 1620s, by folk-etymology supposed to be because the cut of beef was "knighted" by an English king for its superiority, a tale variously told of Henry VIII, James I, and Charles II. The story dates to 1655.
sirocco (n.): "hot wind blowing from the Libyan deserts," 1610s, from Italian sirocco, from vulgar Arabic shoruq "the east wind," from Arabic sharqi "eastern, east wind," from sharq "east," from sharaqa "to rise" (in reference to the sun).
sirrah: 1520s, term of address used to men or boys expressing anger or contempt, archaic extended form of sir (in U.S., siree, attested from 1823).
sis (n.): 1650s, abbreviated form of sister; in American English, applied generally to girls and young women (1859). It also was the familiar short form of Cecilie, Cicely, a common name for girls in the Middle English period.
sis-boom-bah: cheerleading chant, originally (1867) an echoic phrase imitating the sound of a skyrocket flight (sis), the burst of the fireworks (boom), and the reaction of the crowd ((b)ah).
sisal (n.): 1883, short for Sisal hemp or grass (1843), from Sisal, port in Yucatan, from which the rope-making fiber was exported.
sissify (v.): 1897 (implied in sissified), American English, from sissy + -fy. Related: Sissifying; sissification (1915).
sissy (n.): 1846, "sister," extended form of sis (q.v.). Meaning "effeminate man" is recorded from 1887; the adjective in this sense is from 1891. Related: Sissiness. Sissy bar is recorded from 1969.
sist: legal term, from Latin sistere "to cause to stand" (see assist (v.)).
sister (n.): mid-13c., from Old English sweostor, swuster "sister," or a Scandinavian cognate (Old Norse systir, Swedish syster, Danish søster), in either case from Proto-Germanic *swestr- (source also of Old Saxon swestar, Old Frisian swester, Middle Dutch suster, Dutch zuster, Old High German swester, German Schwester, Gothic swistar).

These are from PIE *swesor, one of the most persistent and unchanging PIE root words, recognizable in almost every modern Indo-European language (Sanskrit svasar-, Avestan shanhar-, Latin soror, Old Church Slavonic, Russian sestra, Lithuanian sesuo, Old Irish siur, Welsh chwaer, Greek eor). French soeur "a sister" (11c., instead of *sereur) is directly from Latin soror, a rare case of a borrowing from the nominative case.

According to Klein's sources, probably from PIE roots *swe- "one's own" + *ser- "woman." For vowel evolution, see bury. Used of nuns in Old English; of a woman in general from 1906; of a black woman from 1926; and in the sense of "fellow feminist" from 1912. Meaning "female fellow-Christian" is from mid-15c. Sister act "variety act by two or more sisters" is from vaudeville (1908).
sister-in-law (n.): mid-15c.; see sister + in-law.
sisterhood (n.): "state of being a sister," late 14c., from sister + -hood. Meaning "a society of sisters" (usually a religious order) is from 1590s; sense of "women having some common characteristic or calling" is from c. 1600.
sisterly (adj.): 1560s, from sister + -ly (1). Related: Sisterliness.
Sistine (adj.): 1769, literally "pertaining to Pope Sixtus," from Italian sistino, from Sixtus, name of five popes, from Latin sextus "sixth" (see Sextus). The "chapel" is named for Sixtus IV (Francesco della Rovere), pope 1471-84, who had it built. The painting by Raphael known as the Sistine Madonna is so called because it also shows Sixtus II, a 3c. martyr and saint; it is better known now for the two cherubs at the bottom of the picture who by 1900 were well-known in isolation from the rest of the picture in engravings, etc.
Sisyphean (adj.): "pertaining to or resembling the unceasingly recurring and fruitless labors of Sisyphus," 1630s, from Sisyphus + -an. Earlier Sisyphian (1590s).
Sisyphus: King of Corinth, famed as "the craftiest of men," he was condemned in the afterlife to roll uphill a stone which perpetually rolls down again; Greek Sisyphos, a name of unknown origin. Liddell & Scott suggest a reduplication of syphos "the crafty" (with Aeolic -u- for -o-), but Klein calls this folk-etymology.
sit (v.): Old English sittan "to occupy a seat, be seated, sit down, seat oneself; remain, continue; settle, encamp, occupy; lie in wait; besiege" (class V strong verb; past tense sæt, past participle seten), from Proto-Germanic *setjan (source also of Old Saxon sittian, Old Norse sitja, Danish sidde, Old Frisian sitta, Middle Dutch sitten, Dutch zitten, Old High German sizzan, German sitzen, Gothic sitan), from PIE root *sed- (1) "to sit" (see sedentary).

With past tense sat, formerly also set, now restricted to dialect, and sate, now archaic; and past participle sat, formerly sitten. In reference to a legislative assembly, from 1510s. Meaning "to baby-sit" is recorded from 1966.

To sit back "be inactive" is from 1943. To sit on one's hands was originally "to withhold applause" (1926); later, "to do nothing" (1959). To sit around "be idle, do nothing" is 1915, American English. To sit out "not take part" is from 1650s. Sitting pretty is from 1916.
sit-down (adj.): 1836 of meals, 1936 of strikes, from verbal phrase (c. 1200), from sit (v.) + down (adv.); as a noun, sit-down "act of sitting down" is from 1861.
sit-in: 1936, in reference to session musicians; 1937, in reference to union action; 1941, in reference to student protests. From the verbal phrase; see sit (v.) + in (adv.). To sit in is attested from 1868 in the sense "attend, be present;" from 1919 specifically as "attend as an observer."
sit-up (n.): also situp, kind of physical exercise, 1955, from the verbal phrase (attested from early 13c.); see sit (v.) + up (adv.). Related: Sit-ups.
sitar (n.): 1845, from Hindi sitar, from Persian sitar "three-stringed," from si "three" (Old Persian thri-; see three) + tar "string" (see tenet).
sitcom (n.): by 1959, from the first elements of situation comedy, a phrase attested from 1953 of television shows, 1943 of radio programs; see situation.
Even Bing Crosby has succumbed to series TV and will appear in a sitcom as an electrical engineer who happens to break into song once a week. ["Life," Sept. 18, 1964]
site (n.): "place or position occupied by something," especially with reference to environment, late 14c., from Anglo-French site, Old French site "place, site; position," and directly from Latin situs "a place, position, situation, location, station; idleness, sloth, inactivity; forgetfulness; the effects of neglect," from past participle of sinere "let, leave alone, permit," from PIE *si-tu-, from root *tkei- "to settle, dwell, be home" (see home (n.)).