Online Etymology Dictionary

sidetrack (n.): "railway siding," 1835, from side (adj.) + track (n.). The verb meaning "to move (a train car) onto a sidetrack" is from 1880; figurative sense of "to divert from the main purpose" is attested from 1889. Related: Sidetracked.
sidewalk (n.): "path for pedestrians on the side of a street," 1739, from side (adj.) + walk (n.).
sideways: 1570s, from side (n.). To look sideways "cast scornful glances" is recorded from 1844.
sidewinder (n.): species of rattlesnake, 1875, American English, from side + agent noun of wind (v.), so called in reference to its "peculiar lateral progressive motion."
Sidhe: "the hills of the fairies," 1793; but in Yeats, "the fairie folk" (1899), elipsis of Irish (aos) sidhe "people of the faerie mound" (cf. second element in banshee).
siding (n.): c.1600, "a taking of sides in a conflict or debate," from side (q.v.). First attested 1825 in the railroad sense; 1829 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" (early 14c.), from side + adv. suffix -ling; altered on analogy of verbs ending in -le. Related: Sidled; sidling.
Sidon: ancient Phoenician city, from Greek Sidon, from Phoenician Tzidhon, literally "fishing place," from tzud "to hunt, to capture."
SIDS: 1970, acronym for Sudden Infant Death Syndrome.
Sieg Heil: Nazi salute, German, literally "hail victory;" from German Sieg "victory," from Old High German sigu, from Proto-Germanic *sigiz- "victory" (cf. Middle Dutch seghe, Old Norse sigr, Old English sige), from PIE root *segh- "to have, to hold" (cf. Sanskrit saha- "victory," sahate "overcomes, masters;" see scheme (n.)). For second element, see health.
siege (n.): early 13c., "a seat" (as in Siege Perilous, early 13c., the vacant seat at Arthur's Round Table, 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 Line: World War I German fortifications in France, from German Siegfriedlinie, named for the hero in Wagner's "Ring" cycle. The name is a compound of words meaning "victory" + "protection."
sienna: 1760, from Italian terra di Sienna "earth of Siena," city in central Italy, where the coloring material was first produced. The city name probably is from Senones, the name of a Gaulish people who settled there in ancient times.
sierra (n.): "a range of hills," 1610s, from Spanish sierra "jagged mountain range," literally "saw," from Latin serra "a saw," 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.
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 *sibi (cf. Middle Dutch seve, Dutch zeef, Old High German sib, German Sieb), of unknown origin. Related to sift. Sieve and shears formerly were used in divinations.
sieve (v.): late 15c., from sieve (n.). Related: Sieved; sieving.
sift: Old English siftan "pass something through a sieve," related to sife (see sieve). Cf. Dutch ziften, Middle Low German sichten, German sichten "to sift." Metaphoric sense of "look carefully through" first recorded 1530s.
sig: abbreviation of signature, 1866.
sigh: c.1300 (n. and v.), probably a back-formation from sighte, past tense of Old English sican "to sigh," perhaps echoic of the sound of sighing.
sight (n.): Old English gesiht, gesihð "thing seen," from Proto-Germanic *sekh(w)- (cf. Danish sigte, Swedish sigt, Middle Dutch sicht, Dutch zicht, Old High German siht, German Sicht, Gesicht), stem of Old English seon (see see (v.)). Meaning "perception or apprehension by means of the eyes" is from early 13c.
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 "device on a firearm to assist in aiming" is from 1580s; the verb in this sense is from 1842. Related: Sighted; sighting. Sight for sore eyes "welcome visitor" is attested from 1738; sight unseen "without previous inspection" is from 1892. Sight gag first attested 1944.
sights: "features of a place that are deemed worth seeing," 1630s, from sight.
sightseeing: 1824, from sight (cf. sights) + present participle of see. Sight-seer first recorded 1834.
sigil (n.): "sign," c.1600, from Late Latin sigillum, from Latin sigilla (neuter plural), 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" + munt "hand, protection," from PIE *man- "hand" (see manual (adj.)).
sigma: 18th letter of the Greek alphabet, corresponding to Latin S; in uncial writing, shaped like an S or a C.
sigmoid (adj.): "shaped like a C" (1660s) or "shaped like an S" (1786), from sigma + -oid. Especially of the flexure of the colon (1891).
sigmoidoscopy (n.): 1900, from sigmoid + -oscopy (see -scope).
sign (n.): early 13c., "gesture or motion of the hand," from Old French signe "sign, mark, signature," from Latin signum "mark, token, indication, symbol," from PIE root *sekw- "point out" (see see).

Meaning "a mark or device having some special importance" is recorded from late 13c.; that of "a miracle" is from c.1300. Sense of "characteristic device attached to the front of an inn, shop, etc., to distinguish it from others" is first recorded mid-15c. Ousted native token. In some uses, the word probably is a shortening of ensign. Sign language is recorded from 1847; earlier hand-language (1670s).
sign (v.): c.1300, "to make the sign of the cross," from Old French signer, from Latin signare, 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 sign language" is recorded from 1700. Related: Signed; signing.
signage (n.): 1972, in reference to signs on roads or outside stores, from sign (n.) + -age. Earlier in legal language with reference to affixing signatures.
signal (n.): late 14c., from Old French signal, from Medieval Latin signale "a signal," from Late Latin signalis (adj.) "used as a signal, pertaining to a sign," from Latin signum "signal, sign" (see sign (n.)).
signal (v.): 1805, from signal (n.). Related: Signaled; signaling. Earlier verb was signalize (1650s).
signal (adj.): "remarkable, striking, notable" 1641, from French signalé, past participle of signaler "to distinguish" (see signal (n.)).
signatory: 1640s, "used in sealing" (adj.), from Latin signatorius "of sealing," from signatus, past participle of signare "to sign" (see sign (v.)). Noun sense of "one who signs" first recorded 1866.
signature (n.): 1530s, a kind of document in Scottish law, from Middle French signature (16c.), from Medieval Latin signatura "sign," in classical Latin "the matrix of a seal," from signatus, past participle of signare "to mark, sign" (see sign (v.)). Meaning "one's own name written in one's own hand" is from 1570s, replacing sign-manual (early 15c.) in this sense.
signee (n.): 1953, from sign (v.) + -ee.
signer (n.): 1610s, agent noun from sign (v.). In American history, with reference to the Declaration of Independence, by 1865.
signet (n.): late 14c., "small seal" (especially one on a finger ring), from Old French signet "a small seal," diminutive of signe "sign" (see sign (n.)).
significance: c.1300, from Latin significantia "meaning, force, energy," from significans, present participle of significare (see signify).
significant (adj.): 1570s, from Latin significant-, stem of significans, present participle of significare (see signify). Earlier in the same sense was significative (c.1400). Related: Significantly. Significant other (n.) attested by 1961, in psychology, "the most influential other person in the patient's world."
signification: early 14c., "symbolization, representation," from Old French signification or directly from Latin significationem (nominative significatio), noun of action from past participle stem of significare (see signify). From late 14c. as "meaning" (of a word, etc.).
signifier: 1530s, agent noun from signify.
signify (v.): mid-13c., from Old French signifier (12c.), from Latin significare "to show by signs, mean, signify," from significus (adj.), from signum "sign" (see sign (n.)) + root of facere "to make" (see factitious). Intransitive sense of "to be of importance" is attested from 1660s. Meaning "engage in mock-hostile banter" is American English black slang first recorded 1932.
...'signifying,' which in Harlemese means making a series of oblique remarks apparently addressed to no one in particular, but unmistakable in intention in such a close-knit circle. ["Down Beat," March 7, 1968]
signor: 1570s, from Italian signore, from Latin seniorem, accusative of senior (see senior). Feminine form signora is from 1636; diminutive signorina is first recorded 1820.
signpost (n.): 1610s, "sign on a post, usually indicating an inn or shop," from sign (n.) + post (n.1). Meaning "guide- or direction-post along a road" is attested from 1863. Figurative sense is from 1889.
signup: 1940, from sign (v.) + up.
sike (n.): "small stream," Old English sic.
Sikh: 1781, sect established 16c. in Punjab by Nanak Shah, from Hindi sikh "disciple," from Sanskrit siksati "studies, learns," related to saknoti "he is able, he is strong."