Online Etymology Dictionary

sidearms (n.): also side-arms, 1760, from side (adj.) + plural of arm (n.2).
sidebar (n.): "secondary article accompanying a larger one in a newspaper," 1948, from side (adj.) + bar (n.1).
sideboard (n.): "table placed near the side of a room or hall" (especially one where food is served), c. 1300, from side (adj.) + board (n.1).
sideburns (n.): 1880, American English, alteration of burnsides (q.v).
sidekick (n.): also side-kick, "companion or close associate," 1901, also side-kicker (1903), American English, of unknown origin. Earlier terms were side-pal (1886), side-partner (1886).
sidelight (n.): also side-light, c. 1600, "light coming from the side," from side (adj.) + light (n.). Figurative meaning "incidental information on a subject" is attested from 1862.
sideline (n.): also side-line, "line on the side of a fish," 1768; "lines marking the limits of playing area" (on a football field, etc.), 1862, from side (adj.) + line (q.v.). Meaning "course of business aside from one's regular occupation" is from 1890. Railway sense is from 1890. The figurative sense of "position removed from active participation" is attested from 1934 (from the railway sense or from sports, because players who are not in the game stand along the sidelines). The verb meaning "put out of play" is from 1945. Related: Sidelined; sidelining.
sidelong (adv.): "towartd the side," 1570s, alteration of Middle English sidlyng (see sidle), probably by influence of side (n.) + long (adj.). As an adjective from 1590s.
sideman (n.): "supporting musician," 1936, from side (adj.) + man (n.). Earlier it meant "assistant to a church warden" (1560s).
sidenote (n.): 1776, from side (adj.) + note (n.).
sidereal (adj.): also siderial, 1630s, "star-like;" 1640s, "of or pertaining to the stars," earlier sideral (1590s), from French sidereal (16c.), from Latin sidereus "starry, astral, of the constellations," from sidus (genitive sideris) "star, group of stars, constellation," probably from PIE root *sweid- "to shine" (source also of Lithuanian svidus "shining, bright"). Sidereal time is measured by the apparent diurnal motion of the fixed stars. The sidereal day begins and ends with the passage of the vernal equinox over the meridian and is about four minutes shorter than the solar day, measured by the passage of the sun over the meridian.
sideshow (n.): also side-show, 1855, "minor exhibition alongside or near a principal one," apparently a coinage of P.T. Barnum's, from side (adj.) + show (n.). Hence, any diversion or distracting event.
sidestep (n.): also side-step, 1757, "a stepping to the side" (originally in military drill), from side (adj.) + step (n.). The verb is recorded from 1895; the figurative sense is attested from 1900.
sidetrack (n.): also side-track, "railway siding," 1835, from side (adj.) + track (n.). The verb meaning "to move (a train car) onto a sidetrack" is from 1874; figurative sense of "to divert from the main purpose" is attested from 1881. Related: Sidetracked.
sidewalk (n.): "path for pedestrians on the side of a street," 1739, from side (adj.) + walk (n.). The use of sidewalk for pavement as one of the characteristic differences between American and British English has been noted since at least 1902.
sideways (adv.): 1570s, from side (n.) + way (n.), with adverbial genitive. To look sideways "cast scornful glances" is recorded from 1844.
sidewinder (n.): small horned rattlesnake of southwestern U.S., 1875, American English, from side (adj.) + agent noun of wind (v.1), so called in reference to its "peculiar lateral progressive motion." Also sidewiper (1888).
Sidhe: "the hills of the fairies," 1793; but in Yeats, "the fairie folk" (1899), elipsis of Irish (aos) sidhe "people of the faerie mound" (compare second element in banshee).
siding (n.): c. 1600, "a taking of sides in a conflict or debate," verbal noun from side. First attested 1825 in the railroad sense; 1829, American English, in the architectural sense of "boarding on the sides of a building."
sidle (v.): "to move or go sideways," 1690s, back-formation from obsolete Middle English sidlyng (adv.) "obliquely, sideways; aslant; laterally" (early 14c., perhaps in Old English), from side (n.) + adverbial suffix -ling; altered on analogy of verbs ending in -le. Related: Sidled; sidling. Old English had sidlingweg (n.) "sidelong-way, oblique road."
Sidon: ancient Phoenician city, from Greek Sidon, from Phoenician Tzidhon, literally "fishing place," from tzud "to hunt, to capture." Related: Sidonian.
SIDS (n.): 1970, acronym for Sudden Infant Death Syndrome.
Sieg Heil (interj.): Nazi salute, German, literally "hail victory;" from German Sieg "victory," from Old High German sigu (see Siegfried) + heil "to hail," from Proto-Germanic *hailitho (see health). English heil was used in Middle English as a salutation implying respect or reverence (c. 1200; see hail (interj.)).
siege (n.): early 13c., "a seat" (as in Siege Perilous, early 13c., the vacant seat at Arthur's Round Table, according to prophecy to be occupied safely only by the knight destined to find the Holy Grail), from Old French sege "seat, throne," from Vulgar Latin *sedicum "seat," from Latin sedere "sit" (see sedentary). The military sense is attested from c. 1300; the notion is of an army "sitting down" before a fortress.
Siegfried: masc. proper name, German Siegfried, first element from Old High German sigu "victory," from Proto-Germanic *sigiz- "victory" (source also of Old Frisian si, Old Saxon sigi, Middle Dutch seghe, Dutch zege, German Sieg, Old Norse sigr, Danish seier, Gothic sigis, Old English sige "victory, success, triumph"), from PIE root *segh- "to have, to hold" (source also of Sanskrit saha- "victory," sahate "overcomes, masters;" see scheme (n.)).

Second element from Old High German frithu "peace" (see Frederick). Siegfried Line, World War I German fortifications in France, is from German Siegfriedlinie, named for the hero in Wagner's "Ring" cycle.
Sienna: city in central Italy, probably from Senones, the name of a Gaulish people who settled there in ancient times. Related: Sienese. The brownish-ochre color (1760) is from Italian terra di Sienna "earth of Siena," where the coloring material first was produced.
sierra (n.): "a range of hills," 1610s, from Spanish sierra "jagged mountain range," literally "saw," from Latin serra "a saw" (compare serrated), which is of unknown origin.
Sierra Leone: West African nation, literally "lion mountains," from Spanish sierra "mountain range" (see sierra) + leon "lion" (see lion). Attested from mid-15c. in Portuguese explorers' accounts, and a very early explanation of the name derives it from the "roaring" of thunder in the mountains. Related: Sierra Leonean.
siesta (n.): "mid-day nap," 1650s, from Spanish siesta, from Latin sexta (hora) "sixth (hour)," the noon of the Roman day (coming six hours after sunrise), from sexta, fem. of sextus "sixth" (see Sextus).
sieve (n.): Old English sife "sieve," from Proto-Germanic *sib (source also of Middle Dutch seve, Dutch zeef, Old High German sib, German Sieb), from PIE *seib- "to pour out, sieve, drip, trickle" (see soap (n.)). Related to sift. The Sieve of Eratosthenes (1803) is a contrivance for finding prime numbers. Sieve and shears formerly were used in divinations.
sieve (v.): late 15c., from sieve (n.). Related: Sieved; sieving.
sift (v.): Old English siftan "pass (something) through a sieve," from Proto-Germanic *sib- (source also of Dutch ziften, Middle Low German sichten, German sichten "to sift;" see sieve (n.)). Intransitive sense "to pass loosely or fall scatteredly" is from 1590s. Metaphoric sense of "look carefully through" first recorded 1530s. Related: Sifted; sifting.
sifter (n.): 1570s, agent noun from sift (v.).
sig (n.): abbreviation of signature, 1866.
sigh (v.): mid-13c., probably a Middle English back-formation from sighte, past tense of Old English sican "to sigh," perhaps echoic of the sound of sighing. Related: Sighed; sighing.
sigh (n.): early 14c., from sigh (v.).
sight (n.): Old English sihð, gesiht, gesihð "thing seen; faculty of sight; aspect; vision; apparition," from Proto-Germanic *sekh(w)- (source also of Danish sigte, Swedish sigt, Middle Dutch sicht, Dutch zicht, Old High German siht, German Sicht, Gesicht), stem that also yielded Old English seon (see see (v.)), with noun suffix -th (2), later -t.
Verily, truth is sight. Therefore if two people should come disputing, saying, 'I have seen,' 'I have heard,' we should trust the one who says 'I have seen.' [Brhadaranyaka Upanishad 5.14.4]
Meaning "perception or apprehension by means of the eyes" is from early 13c. Meaning "device on a firearm to assist in aiming" is from 1580s. A "show" of something, hence, colloquially, "a great many; a lot" (late 14c.). Sight for sore eyes "welcome visitor" is attested from 1738; sight unseen "without previous inspection" is from 1892. Sight gag first attested 1944. Middle English had sighty (late 14c.) "visible, conspicuous; bright, shining; attractive, handsome;" c. 1400 as "keen-sighted;" mid-15c. as "discerning" (compare German sichtig "visible").
sight (v.): 1550s, "look at, view, inspect," from sight (n.). From c. 1600 as "get sight of," 1842 as "take aim along the sight of a firearm." Related: Sighted; sighting.
sighting (n.): "instance of catching sight," 1853, verbal noun from sight (v.).
sightless (adj.): late 13c., from sight (n.) + -less. Related: Sightlessly; sightlessness.
sights (n): "features of a place that are deemed worth seeing," 1630s, plural of sight (n.).
sightseeing (n.): also sight-seeing, 1821, from sight (see sights) + present participle of see (v.). Sight-see (v.) is from 1824. Sight-seer first recorded 1821.
sigil (n.): "a sign, mark, or seal," mid-15c., from Late Latin sigillum, from Latin sigilla (neuter plural) "statuettes, little images, seal," diminutive of signum "sign" (see sign (n.)). In astrology, an occult device supposed to have great power (1650s).
When my mistress died, she had under her arm-hole a small scarlet bag full of many things, which, one that was there delivered unto me. There was in this bag several sigils, some of Jupiter in Trine, others of the nature of Venus, some of iron, and one of gold, of pure angel-gold, of the bigness of a thirty-three shilling piece of King James's coin. ["The Antiquarian Repertory," London, 1780]
Sigismund: masc. proper name, from German, literally "protection through victory," from Old High German sigu "victory" (see Siegfried) + munt "hand, protection," from PIE *man- "hand" (see manual (adj.)).
sigma: 18th letter of the Greek alphabet, corresponding to Latin S, a metathesis of Hebrew samekh. In uncial writing, shaped like an S or a C.
sigmatism (n.): 1888, "difficulty in pronouncing 'S,'" from comb. form of sigma + -ism. As "use or recurrence of 'S'" from 1889.
sigmoid (adj.): "shaped like a C" (1660s) or "shaped like an S" (1786), from sigma (q.v.) + -oid. Especially of the flexure of the colon (1891).
sigmoidoscopy (n.): 1896, from sigmoid + -scopy, with connective -o-.
sign (v.): c. 1300, "to make the sign of the cross," from Old French signier "to make a sign (to someone); to mark," from Latin signare "to set a mark upon, mark out, designate; mark with a stamp; distinguish, adorn;" figuratively "to point out, signify, indicate," from signum (see sign (n.)). Sense of "to mark, stamp" is attested from mid-14c.; that of "to affix one's name" is from late 15c. Meaning "to communicate by hand signs" is recorded from 1700. Related: Signed; signing.
sign (n.): early 13c., "gesture or motion of the hand," especially one meant to communicate something, from Old French signe "sign, mark," from Latin signum "identifying mark, token, indication, symbol; proof; military standard, ensign; a signal, an omen; sign in the heavens, constellation," according to Watkins, literally "standard that one follows," from PIE *sekw-no-, from root *sekw- (1) "to follow" (see sequel).

Ousted native token. Meaning "a mark or device having some special importance" is recorded from late 13c.; that of "a miracle" is from c. 1300. Zodiacal sense in English is from mid-14c. Sense of "characteristic device attached to the front of an inn, shop, etc., to distinguish it from others" is first recorded mid-15c. Meaning "token or signal of some condition" (late 13c.) is behind sign of the times (1520s). In some uses, the word probably is a shortening of ensign. Sign language is recorded from 1847; earlier hand-language (1670s).