Online Etymology Dictionary

swagger (v.): 1580s, "to strut in a defiant or insolent manner;" earliest recorded usages are in Shakespeare ("Midsummer Night's Dream," "2 Henry IV," "King Lear"), probably a frequentative form of swag (v.) "to sway." Meaning "to boast or brag" is from 1590s. Related: Swaggered; swaggering. The noun is attested from 1725.
swaggerer (n.): 1590s, agent noun from swagger (v.).
Swahili: name of a Bantu people inhabiting the coast of southeastern Africa, 1814, literally "coast-dwellers," from Arabic sawahil, plural of sahil "coast" + ethnic suffix -i.
swain (n.): mid-12c., "young man attendant upon a knight," from Old Norse sveinn "boy, servant, attendant," from Proto-Germanic *swainaz "attendant, servant," properly "one's own (man)," from PIE *swoi-no-, from root *s(w)e- "oneself, alone, apart" (see idiom). Cognate with Old English swan "shepherd, swineherd," Old Saxon swen, Old High German swein. Meaning "country or farm laborer" is from 1570s; that of "lover, wooer" (in pastoral poetry) is from 1580s.
SWAK: acronym for sealed with a kiss, attested from 1911, in a legal publication quoting a letter from 1909:
"... Well Kid I don't know nothing else to say only that I hope to see your sweet face Sat. Good by from your Dear Husban to his sweet little wife. P. S. excuse bad writing and mispelled words take all mistakes as kisses. S.W.A.K. * * *" This letter was postmarked at Des Moines October 20, 1909, addressed to Carrie Sprague at Jefferson, Iowa, and reached the latter place October 21, 1909. [State v. Manning (a conspiracy-to-lure-women-to-prostitution case), Supreme Court of Iowa, Nov. 16, 1910, reported in "Northwestern Reporter," Volume 128, 1911]
Popularized in soldiers' letters home in World War I. It probably is meant also to echo the sound of a kiss. Compare Middle English swack "a hard blow" (late 14c.).
swale (n.): "low, hollow place, often boggy," 1580s, special use of Scottish swaill "low, hollow place," or East Anglian dialectal swale "shady place" (mid-15c.); both probably from Old Norse svalr "cool," from Proto-Germanic *swalaz. A local word in England, in U.S. given broad application, especially to the lower tracts of the prairie and recently to landscaping features in suburban developments.
swallow (v.): "ingest through the throat" (transitive), Old English swelgan "swallow, imbibe, absorb" (class III strong verb; past tense swealg, past participle swolgen), from Proto-Germanic *swelgan/*swelhan (source also of Old Saxon farswelgan, Old Norse svelgja "to swallow," Middle Dutch swelghen, Dutch zwelgen "to gulp, swallow," Old High German swelahan "to swallow," German schwelgen "to revel"), probably from PIE root *swel- (1) "to eat, drink" (source also of Iranian *khvara- "eating").

Intransitive sense "perform the act of swallowing" is from c. 1700. Sense of "consume, destroy" is attested from mid-14c. Meaning "to accept without question" is from 1590s. Related: Swallowed; swallowing.
swallow (n.1): type of migratory bird (family Hirundinidae), Old English swealwe "swallow," from Proto-Germanic *swalwon (source also of Old Saxon, Old Norse, Old Frisian, Swedish svala, Danish svale, Middle Dutch zwalewe, Dutch zwaluw, Old High German swalawa, German Schwalbe), from PIE *swol-wi- (source also of Russian solowej, Slovak slavik, Polish słowik "nightingale"). The etymological sense is disputed. Popularly regarded as harbingers of summer; swallows building nests on or near a house is considered good luck.
swallow (n.2): "an act of swallowing," 1822, from swallow (v.). In late Old English and Middle English it meant "gulf, abyss, hole in the earth, whirlpool," also, in Middle English, "throat, gullet." Compare Old Norse svelgr "whirlpool," literally "devourer, swallower." Meaning "as much as one can swallow at once, mouthful" is from 1861.
swallowtail (n.): also swallow-tail, 1540s as a type of arrowhead, from swallow (n.1) + tail (n.). Of a type of butterfly, by 1776; of a type of coat, 1835. As an adjective from 1590s. The bird's tail is long and deeply forked.
swam: past tense of swim (v.).
swami (n.): 1773, "Hindu idol," later, "Hindu religious teacher" (1901), from Hindi swami "master" (used as a term of address to a Brahmin), from Sanskrit svamin "lord, prince, master, (one's own) master," from sva-s "one's own" (from PIE *s(u)w-o- "one's own," from root *s(w)e-; see idiom) + amah "pressure, vehemence."
swamp (n.): c. 1500 (implied in swampwatyr "swamp-water"), of uncertain origin, perhaps [Barnhart] a dialectal survival from an Old English cognate of Old Norse svöppr "sponge, fungus," from Proto-Germanic *swampuz; but traditionally connected with Middle English sompe "morass, swamp," which probably is from Middle Dutch somp or Middle Low German sump "swamp" (see sump). All of these likely are ultimately related to each other, from PIE *swombho- "spongy; mushroom," via the notion of "spongy ground."
[B]y swamps then in general is to be understood any low grounds subject to inundations, distinguished from marshes, in having a large growth of timber, and much underwood, canes, reeds, wythes, vines, briers, and such like, so matted together, that they are in a great measure impenetrable to man or beast .... [Bernard Romans, "A Concise History of East and West Florida," 1775]
More popular in U.S. (swamp (n.) by itself is first attested 1624 in Capt. John Smith's description of Virginia). Swamp-oak is from 1680s, American English. Swamp Yankee "rural, rustic New Englander" is attested from 1941. Thornton's "American Glossary" (1912) has swamp-angel "dweller in a swamp," swamp-law "might makes right."
swamp (v.): "overwhelm, sink (as if in a swamp)," 1772, from swamp (n.). Figurative sense is from 1818. Related: Swamped; swamping.
swamp-land (n.): 1660s, from swamp (n.) + land (n.).
swamper (n.): 1735, "one who lives in a swampy district," from swamp (n.). Meaning "workman who clears a lumber road through swamp or forest" is 1857, American English; meaning "all-purpose assistant in a restaurant or saloon" is from 1907.
swampy (adj.): 1690s, from swamp (n.) + -y (2). Related: Swampiness.
swan (n.): Old English swan "swan," from Proto-Germanic *swanaz "singer" (source also of Old Saxon swan, Old Norse svanr, Danish svane, Swedish svan, Middle Dutch swane, Dutch zwaan, Old High German swan, German Schwan), probably literally "the singing bird," from PIE root *swen- "to sing, make sound" (see sound (n.1)); thus related to Old English geswin "melody, song" and swinsian "to make melody."

In classical mythology, sacred to Apollo and to Venus. The singing of swans before death was alluded to by Chaucer (late 14c.), but swan-song (1831) is a translation of German Schwanengesang. The ancient Indo-European mythical swan-maiden so called by mythographers from 1829. Swan dive is recorded from 1898. A black swan was proverbial for "something extremely rare or non-existent" (late 14c.), after Juvenal ["Sat." vi. 164], but later they turned up in Australia (Chenopsis atratus).
"Do you say no worthy wife is to be found among all these crowds?" Well, let her be handsome, charming, rich and fertile; let her have ancient ancestors ranged about her halls; let her be more chaste than all the dishevelled Sabine maidens who stopped the war--a prodigy as rare upon the earth as a black swan! yet who could endure a wife that possessed all perfections? I would rather have a Venusian wench for my wife than you, O Cornelia, mother of the Gracchi, if, with all your virtues, you bring me a haughty brow, and reckon up Triumphs as part of your marriage portion. [Juvenal]
Swanee: in Stephen Foster's "Old Folks at Home," river in Georgia and Florida, usually Suwanee, sometimes said to be a corruption of Spanish San Juan [Room]; Bright says the river name is from the Cherokee village of Sawani, for which no etymology is offered.
swang: obsolete past tense of swing (v.).
swank (adj.): "stylish, classy, posh," 1913, from earlier noun or verb; "A midland and s.w. dial. word taken into general slang use at the beginning of the 20th cent." [OED]; compare swank (n.) "ostentatious behavior," noted in 1854 as a Northampton word; swank (v.), from 1809 as "to strut, behave ostentatiously." Perhaps ultimately from Proto-Germanic *swank-, from PIE *sweng(w)-, a Germanic root meaning "to swing, turn, toss" (source also of Middle High German swanken "to sway, totter, turn, swing," Old High German swingan "to swing;" see swing (v.)). Perhaps the notion is of "swinging" the body ostentatiously (compare swagger).

A separate word-thread derives from Old English swancor "pliant, bending," and from this comes swanky (n.) "active or clever young fellow" (c. 1500).
swanky (adj.): "imposing, stylish," 1842, from swank + -y (2). Related: swankiness.
Swansea: a Scandinavian name, probably literally "Sveinn's Island."
swap (v.): c. 1200, "to strike, strike the hands together," of uncertain origin, possibly imitative of the sound of hitting or slapping. The sense of "to exchange, barter, trade" is first recorded 1590s, possibly from the notion of slapping hands together as a sign of agreement in bargaining (as in strike a bargain). Related: Swapped; swapping. The noun in this sense is attested from 1620s; earlier "a striking, an act of striking" (mid-13c.). Swap-meet attested from 1968, American English.
sward (n.): "grass-covered ground," c. 1300, from Old English sweard "skin, hide, rind" (of bacon, etc.), from Proto-Germanic *swarthu- (source also of Old Frisian swarde "skin of the head," Middle Dutch swarde "rind of bacon," Dutch zwoord "rind of bacon," German Schwarte "thick, hard skin, rind," Old Norse svörðr "walrus hide"). Meaning "sod, turf" developed from the notion of the "skin" of the earth (compare Old Norse grassvörðr, Danish grønsvær "greensward").
sware: obsolete or archaic past tense of swear (v.), common 15c.-17c. by analogy of past tense of bear (v.).
swarf (n.): "grit from a grinding tool," 1560s, perhaps ultimately from Old English geswearf "filings," from sweorfan, or from a Scandinavian source akin to Old Norse svarf "file dust," related to sverfa "to file," from PIE *swerbh- "to turn, wipe off" (see swerve (v.)). Later used of the material cut out to make grooves of gramophone records (1935).
swarm (n.): "cloud of bees or other insects," Old English swearm "swarm, multitude," from Proto-Germanic *swarmaz (source also of Old Saxon, Middle Low German swarm, Danish sværm "a swarm," Swedish svärm, Middle Dutch swerm, Old High German swaram, German Schwarm "swarm;" Old Norse svarmr "tumult"), by Watkins, etc., derived from PIE imitative root *swer- (2) "to buzz, whisper" (see susurration) on notion of humming sound, and thus probably originally of bees. But OED suggests possible connection with base of swerve and ground sense of "agitated, confused, or deflected motion." General sense "large, dense throng" is from early 15c.
swarm (v.1): "to climb (a tree, pole, etc.) by clasping with the arms and legs alternately, to shin," 1540s, of uncertain origin. "Perh. orig. a sailor's word borrowed from the Continent, but no trace of the meaning has been discovered for phonetically corresponding words" [OED]. perhaps originally a sailors' word, of uncertain origin. Also recorded as swarve (16c.) and in Northern dialects swarble, swarmle. Related: Swarmed; swarming.
swarm (v.2): "to leave a hive to start another," also "to gather in a swarm, crowd, or throng," late 14c., from swarm (n.). Compare Dutch zwermen, German schwärmen, Danish sværme. Related: Swarmed; swarming.
swart (adj.): Old English sweart "black, dark," of night, clouds, also figurative, "wicked, infamous," from Proto-Germanic *swarta- (source also of Old Frisian, Old Saxon, and Middle Dutch swart, Dutch zwart, Old Norse svartr, German schwarz, Gothic swarts "dark-colored, black"), from PIE root *swordo- "dirty, dark, black" (source of sordid). The true Germanic word, surviving in the Continental languages, displaced in English by black. Of skin color of persons from late 14c. Related: Swartest.
swarthy (adj.): "dark-colored," especially of skin, 1580s, unexplained alteration of swarty (1570s), from swart + -y (2). Related: Swarthiness.
swash (n.): 1530s, "the fall of a heavy body or blow," probably imitative. It also meant "pig-wash, filth, wet refuse" (1520s) and may have been imitative of the sound of water dashing against solid objects. The meaning "a body of splashing water" is first found 1670s; that of "a dashing or splashing" is from 1847. Swash-letters (1883) are italic capitals with flourished projections.
swash (v.): 1580s, "spill or splash (water) about," 1530s, possibly from wash (v.) with an intensifying s-, or imitative of the sound of water dashing against solid objects. Related: Swashed; swashing.
swashbuckle (v.): 1897, back-formation from swashbuckling.
swashbuckler (n.): also swash-buckler, 1550s, "blustering, swaggering fighting man" (earlier simply swash, 1540s), from swash "fall of a blow" (see swash) + buckler "shield." The original sense seems to have been "one who makes menacing noises by striking his or an opponent's shield."
swashbuckling (adj.): 1690s, adjective formed to go with swashbuckler (q.v.).
swastika (n.): Greek cross with arms bent at right angles, 1871 (in English specifically as emblem of the Nazi party from 1932), from Sanskrit svastika-s, literally "being fortunate," from svasti-s "well-being, luck," from su- "well" (from PIE *(e)su- "good") + as-, root of asti "(he) is," which is from the same PIE root as Latin esse "to be" (see essence).

Also known as gammadion (Byzantine), cross cramponnee (heraldry), Thor's hammer, and, perhaps, fylfot. Originally an ancient cosmic or religious symbol thought to bring good luck. Use in reference to the Nazi emblem first recorded in English in 1932. The German word was Hakenkreuz, literally "hook-cross."
swat (v.): 1796, American English and northern England dialect word, possibly an alteration of Middle English swap "to strike, smite" (see swap), ultimately of imitative origin. Related: Swatted; swatting. The noun is recorded from 1800.
swatch (n.): 1510s, "the countercheck of a tally" (Northumberland dialect), later "a tally attached to cloth sent to be dyed" (1610s, in Yorkshire), of unknown origin. Century Dictionary compares swath. Meaning "a sample piece of cloth" is from 1640s.
swath (n.): Old English swæð, swaðu "track, footstep, trace, scar, vestige," from Proto-Germanic *swathan, *swatho (source also of Old Frisian swethe "boundary made by a scythe," Middle Dutch swade, Dutch zwade, German Schwad "a row of cut grass"); of uncertain origin. Meaning "a mown crop lying on the ground" is from early 14c.; that of "space covered by the single cut of a scythe" emerged late 15c., and that of "a strip, lengthwise extent" is from c. 1600.
swathe (v.): "to bind with bandages, swaddle, wrap," Old English swaþian "to swathe, wrap up," from swaðu "track, trace" (see swath). The noun meaning "infant's swaddling bands" was found in Old English as swaþum (dative plural). Related: Swathed; swathing.
swatter (n.): "instrument for swatting flies," 1906, agent noun from swat (v.).
sway (v.): early 14c., "move, go, go quickly; move (something) along, carry," probably from a Scandinavian source akin to Old Norse sveigja "to bend, swing, give way," Old Danish svegja, perhaps merged with an unrecorded Old English cognate. The whole group might be related to swag (v.) and swing (v.).

The sense of "swing, waver, move in a swaying or sweeping motion" is from late 14c. Meaning "move from side to side" is from c. 1500; transitive sense "cause to move from side to side" is from 1550s (according to OED, not common before 19c.). Figurative sense "cause to be directed toward one side, prejudice" is from 1590s. Related: Swayed; swaying.
sway (n.): c. 1300, "movement from side to side," from sway (v.). The meaning "controlling influence" (as in to be under the sway of) is from 1510s, from a transitive sense of the verb in Dutch and other languages.
sway-backed (adj.): 1670s, according to OED of Scandinavian origin, perhaps related to obsolete Danish sveibaget. See sway (v.) + back (n.).
swear (v.): Old English swerian "take an oath" (class VI strong verb; past tense swor, past participle sworen), from Proto-Germanic *swarjan-, (source also of Old Saxon swerian, Old Frisian swera, Old Norse sverja, Danish sverge, Middle Dutch swaren, Old High German swerien, German schwören, Gothic swaren "to swear"), from PIE root *swer- (1) "to speak, talk, say" (source also of Old Church Slavonic svara "quarrel," Oscan sverrunei "to the speaker").

Also related to the second element in answer. The secondary sense of "use bad language" (early 15c.) developed from the notion of "invoke sacred names." Swear off "desist as with a vow" is from 1898. Swear in "install in office by administration of an oath" is from 1700 in modern use, echoing Old English.
swear-word (n.): 1873, American English colloquial, from swear (v.) + word (n.).
swearing (n.): "utterance of profane language," mid-14c., verbal noun from swear (v.).
sweat (v.): Old English swætan "perspire," also "work hard," from Proto-Germanic *swaitjan "to sweat," from the source of sweat (n.). Compare Frisian swette, Dutch zweeten, Danish svede, German schwitzen. Meaning "to be worried, vexed" is recorded from c. 1400. Transitive sense is from late 14c. Related: Sweated; sweating. Sweating sickness was a sudden, often-fatal fever, accompanied by intense sweating, that struck England 1485 and returned periodically through mid-16c., described in the original citation (a chronicle from 1502) as "a grete deth and hasty."