sweltry (adj.)
1570s, for *sweltery, from swelter (v.) + -y (2).
past participle of sweep (v.).
swerve (v.)
c.1200, "to depart, go make off; turn away or aside;" c.1300, "to turn aside, deviate from a straight course;" in form from Old English sweorfan "to rub, scour, file away, grind away," but sense development is difficult to trace. The Old English word is from Proto-Germanic *swerb- (cf Old Norse sverfa "to scour, file," Old Saxon swebran "to wipe off"), from PIE root *swerbh- "to turn; wipe off." Cognate words in other Germanic languages (cognates: Old Frisian swerva "to creep," Middle Dutch swerven "to rove, roam, stray") suggests the sense of "go off, turn aside" might have existed in Old English, though unrecorded. Related: Swerved; swerving.
swerve (n.)
1741, from swerve (v.).
swift (adj.)
Old English swift "moving quickly," perhaps originally "turning quickly," from Proto-Germanic swip- (see swivel (n.)). Related: Swiftly; swiftness.
swift (n.)
type of bird (several species of the family Cypselidæ, resembling swallows), 1660s, from swift (adj.) in reference to its swift flight. Regarded as a bird of ill-omen, if not downright demonic, probably for its shrill cry. The name earlier had been given to several small fast lizards (1520s).
swig (v.)
1650s, from swig (n.). Related: Swigged; swigging.
swig (n.)
1540s, "a drink, liquor," later "big or hearty drink of liquor" (1620s), of unknown origin.
swill (n.)
"liquid kitchen refuse fed to pigs," 1550s, from swill (v.).
swill (v.)
Old English swilian, swillan "to wash out, gargle," probably from Proto-Germanic *swil-, related to the root of swallow (v.). Meaning "drink greedily" is from 1530s. Related: Swilled; swilling.
swim (v.)
Old English swimman "to move in or on the water, float" (class III strong verb; past tense swamm, past participle swummen), from Proto-Germanic *swimjan (cognates: Old Saxon and Old High German swimman, Old Norse svimma, Dutch zwemmen, German schwimmen), from PIE root *swem- "to be in motion."

The root is sometimes said to be restricted to Germanic, but according to OED possible cognates are Welsh chwyf "motion," Old Irish do-sennaim "I hunt," Lithuanian sundyti "to chase." For the usual Indo-European word, see natatorium. Transitive sense of "cross by swimming" is from 1590s. Sense of "reel or move unsteadily" first recorded 1670s; of the head or brain, from 1702. Figurative phrase sink or swim is attested from mid-15c., in early use often with reference to ordeals of suspected witches.
swim (n.)
1540s, "the clear part of any liquid" (above the sediment), from swim (v.). Meaning "part of a river or stream frequented by fish" (and hence fishermen) is from 1828, and is probably the source of the figurative meaning "the current of the latest affairs or events" (as in in the swim "on the inside, involved with current events," 1869). Meaning "act of swimming" is from 1764.
swimmer (n.)
late 14c., agent noun from swim (v.).
swimmeret (n.)
1840, from swimmer (n.) + diminutive suffix. Related: Swimmerets.
swimming (n.)
late 14c., "act of propelling the body through water," verbal noun from swim (v.). Swimming hole is from 1855, American English; swimming pool is from 1881.
swimmingly (adv.)
"with steady, smooth progress; in an easy, gliding manner," 1620s, from swimming + -ly (2).
swimsuit (n.)
also swim-suit, 1920, from swim + suit (n.).
swindle (v.)
1782, back-formation from swindler "cheater." Related: Swindled; swindling. As a noun, "act of swindling," from 1833.
swindler (n.)
1774, from German Schwindler "giddy person, extravagant speculator, cheat," from schwindeln "to be giddy, act extravagantly, swindle," from Old High German swintilon "be giddy," frequentative form of swintan "to languish, disappear;" cognate with Old English swindan, and probably with swima "dizziness." Said to have been introduced in London by German Jews c.1762.
swine (n.)
Old English swin "pig, hog, wild boar," from Proto-Germanic *swinan (cognates: Old Saxon, Old Frisian Middle Low German, Old High German swin, Middle Dutch swijn, Dutch zwijn, German Schwein, Old Norse, Swedish, Danish svin), neuter adjective (with suffix *-ino-) from PIE *su- "pig" (see sow (n.)). The native word, largely ousted by pig. Applied to persons from late 14c. Phrase pearls before swine (mid-14c.) is from Matt. vii:6; an early English formation of it was:
Ne ge ne wurpen eowre meregrotu toforan eowrum swynon. [c.1000]
The Latin word in the Gospel verse was confused in French with marguerite "daisy" (the "pearl" of the field), and in Dutch the expression became "roses before swine." Swine-flu attested from 1921.
swineherd (n.)
c.1100, swynhyrde; see swine + herd.
swing (v.)
Old English swingan "beat, strike; scourge, flog; to rush, fling oneself" (strong verb, past tense swang, past participle swungen), from Proto-Germanic *swingan (cognates: Old Saxon, Old High German swingan, Old Frisian swinga, German schwingen "to swing, swingle, oscillate"), from PIE *sweng(w)- "to swing, turn, toss" (perhaps Germanic only).

The meaning "move freely back and forth" is first recorded 1540s. Transitive sense "cause to oscillate" is from 1550s. Sense of "bring about, make happen" is from 1934. Sense of "engage in promiscuous sex" is from 1964; earlier, more generally, "enjoy oneself unconventionally" (1957). Related: Swung; swinging. Swing-voter "independent who often determines the outcome of an election" is from 1966.
swing (n.)
Old English swinge "stroke, blow; chastisement," from swing (v.). Meaning "suspended seat on ropes" is from 1680s. Meaning "shift of public opinion" is from 1899. The meaning "variety of big dance-band music with a swinging rhythm" is first recorded 1933, though the sense has been traced back to 1888; its heyday was from mid-30s to mid-40s. Phrase in full swing "in total effect or operation" (1560s) perhaps is from bell-ringing. The backyard or playground swing-set is from 1951.
swing-shift (n.)
1941 (typically 4 p.m. to midnight), from the notion of "facing both ways" between day and night shifts; see swing (v.) + shift (n.).
swinger (n.)
1540s, "one who or that which swings," agent noun from swing (v.). Also (now obsolete) "anything big or great" (1580s). Meaning "person who is sexually promiscuous" is from 1964. Old English swingere (n.) meant "one who strikes, scourger."
swinging (adj.)
1550s, "moving to and fro," present participle adjective from swing (v.). Meaning "marked by a free, sweeping movement" is from 1818. Sense of "uninhibited" is from 1958.
swingle (n.)
"instrument for beating flax," early 14c., from Middle Dutch swinghel "swingle for flax," cognate with Old English swingell "beating, stick to beat, whip, scourge, rod," from swingan "to beat, strike, whip" (see swing (v.)) + instrumental suffix -le. Or perhaps directly from the Old English word, with narrowing of sense.
swingletree (n.)
mid-15c., from swingle "that which swings," from swing (v.) + instrumental suffix -le (compare handle), + tree (n.) in obsolete Middle English sense "pole."
swinish (adj.)
c.1200, originally of persons or behavior, "like a swine; gluttonous, sensual, degraded, beastly," from swine + -ish. Related: Swinishly; swinishness. Similar formation in German schweinisch. Old English had swinlic in same sense.
swipe (v.)
1825, "strike with a sweeping motion," from swipe (n.). The slang sense of "steal, pilfer" appeared 1885, American English; earliest use in prison jargon:
The blokes in the next cell, little Charley Ames and the Sheeney Kid, they was hot to try it, and swiped enough shoe-lining out of shop No. 5, where they worked, to make us all breeches to the stripes. ["Lippincott's Magazine," vol. 35, June 1885]
Meaning "run a credit card" is 1990s. Related: Swiped; swiper; swiping.
swipe (n.)
1807, "a driving stroke made with the arms in full swing," perhaps a dialectal variant of sweep (n.), or in part from obsolete swip "a stroke, blow" (c.1200), from Proto-Germanic *swip-, related to Old English swipu "a stick, whip; chastisement." Other possible sources or influences are Middle English swope "to sweep with broad movements" (in reference to brooms, swords, etc.), from Old English swapan; obsolete swaip "stroke, blow;" or obsolete swape "oar, pole."
swirl (v.)
1510s (transitive), with an isolated instance from 14c.; from swirl (n.). Intransitive sense "form in eddies, whirl in eddies" is from 1755. Related: Swirled; swirling.
swirl (n.)
early 15c., "whirlpool, eddy," originally Scottish, of uncertain origin, perhaps related to dialectal Norwegian svirla or Dutch zwirrelen "to whirl." The meaning "whirling movement" is from 1818.
swirly (adj.)
1785, from swirl (n.) + -y (2).
swish (n.)
1820, sound of something moving through the air, from swish (v.); sense of "effeminate homosexual" is 1930s in homosexual slang, probably from notion of mincing motion. Related: Swishy (adj.).
swish (v.)
1756 (intransitive); 1799 (transitive), probably imitative of the sound made by something brushing against or through something. Related: Swished; swishing.
Swiss (n.)
1510s, from Middle French Suisse, from Middle High German Suizer, from Suiz "Switzerland" (see Switzerland and compare Switzer (1570s), archaic word for "a Swiss," and German Schweiz). As an adjective from 1520s. Swiss banks were notable for assuring anonymity and security by 1949. Swiss cheese is attested from 1808; as a type of something full of holes, from 1924.
switch (n.)
1590s, "slender riding whip," probably from a Flemish or Low German word akin to Middle Dutch swijch "bough, twig," or swutsche, variant of Low German zwukse "long thin stick, switch," from Germanic base *swih- (cognates: Old High German zwec "wooden peg," German Zweck "aim, design," originally "peg as a target," Zwick "wooden peg"), perhaps connected with PIE root *swei- (2) "to swing, bend, to turn."

The meaning "device for changing the direction of something or making or breaking a connection" is first recorded 1797. "The peg sense suits the mech(anical) applications" [Weekley], cognates: switchblade, and these senses in English may be a direct borrowing from those senses in Continental Germanic languages rather than a continuation of the "pliant wand" sense. The meaning "a change from one to another, a reversal, an exchange, a substitution" is first recorded 1920; extended form switcheroo is by 1933.
switch (v.)
1610s, "to strike with a switch," from switch (n.). Related: Switched; switching. The meaning "turn (off or on) with a switch device" is first recorded 1853 of trains on tracks, 1881 of electricity, 1932 of radio or (later) television. Sense of "shift, divert" is from 1860. Meaning "to change one thing for another" is recorded from 1919. Switch-hitter is 1945 in baseball slang; 1956 in the sense of "bisexual person."
switchable (adj.)
1954, from switch (v.) + -able.
switchback (n.)
in reference to zig-zag railways, 1863, from switch (v.) + back (adv.). As an adjective from 1873.
switchblade (n.)
also switch-blade, type of folding pocket knife, 1932, from switch (n.) + blade. So called for the "switch" which is pressed to spring the knife open. Earlier a similar tool was known as an Arkansas toothpick (1837) and a clasp-knife (1755).
switchboard (n.)
also switch-board, "device for making interchangeable connections between many circuits," 1867, from switch (n.) + board (n.1).
named for Schwyz, one of its original cantons. On postage stamps, etc., identified by the Roman name for the region, Helvetia, to avoid having to print the four different forms of the name in the country’s four official languages: Suisse, Schweiz, Svizzera, Svizra.
swivel (n.)
c.1300, "coupling device that allows independent rotation," from frequentative form of stem of Old English verb swifan "to move in a course, revolve, sweep" (a class I strong verb), from Proto-Germanic *swif- (cognates: Old Frisian swiva "to be uncertain," Old Norse svifa "to rove, ramble, drift"), from PIE root *swei- (2) "to turn, bend, move in a sweeping manner."

Related Middle English swive was the principal slang verb for "to have sexual intercourse with," a sense that developed c.1300. This probably explains why, though the root is verbal, the verb swivel is not attested in Modern English until 1794. Compare Middle English phrase smal-swivinge men "men who copulate infrequently."
swivel (v.)
1794 (transitive), from swivel (n.). Intransitive use from 1846. Related: Swiveled; swiveling; swivelled; swivelling.
swivet (n.)
"a fluster," 1867, U.S. dialect, of unknown origin.
swizzle (n.)
1813, name for various kinds of liquor drinks, or for intoxicating drinks generally, possibly a variant of switchel "a drink of molasses and water" (often mixed with rum), first attested 1790, of uncertain origin. As a verb from 1843. Related: Swizzled; swizzling. Swizzle-stick, used for stirring drinks, attested by 1859.
swollen (adj.)
early 14c., past participle adjective from strong conjugation of swell (v.); from Old English geswollen, past participle of swellan.
swoon (n.)
c.1300, suowne, suun, "state of unconsciousness," probably from Old English geswogen "in a faint," past participle of a lost verb *swogan (see swoon (v.)).