Online Etymology Dictionary

span (n.2): "two animals driven together," 1769, from Dutch span, from spannen "to stretch or yoke," from Middle Dutch spannen, cognate with Old English spannen "to join" (see span (v.)).
Spandex: synthetic fiber, 1959, American English, proprietary name, an arbitrary formation from expand.
spandrel (n.): late 15c., "triangular space between the outer curves of an arch," apparently a diminutive of Anglo-French spaundre (late 14c.), perhaps a shortening of espandre "to expand, extend," from Latin expandre (see expand).
spangle (n.): early 15c., diminutive of spang "glittering ornament, spangle," probably from Middle Dutch spange "brooch, clasp," cognate with Old English spang "buckle, clasp," from Proto-Germanic *spango, from an extended form of the root of span (2).
spangle (v.): 1540s, from spangle (n.). Related: Spangled; spangling.
Spanglish (n.): "form of Spanish deformed by English words and idioms," by 1967, probably a nativization of Spanish Espanglish (1954); ultimately from Spanish (n.) + English.
Spaniard: c.1400, from Old French Espaignart, from Espaigne "Spain," from Latin Hispania, from Greek Hispania "Spain," Hispanos "Spanish, a Spaniard," probably from Celt-Iberian, in which (H)i- represents a definite article. The earlier English noun was Spaynol (mid-14c.), from Old French Espaignol.
spaniel (n.): 13c., as a surname meaning "Spaniard;" as a name for a breed of dog of Spanish origin, late 14c., from Old French espagneul, literally "Spanish (dog)," from Vulgar Latin *Hispaniolus "of Spain," diminutive of Latin Hispanus "Spanish, Hispanic" (see Spaniard).
Spanish: c.1200, from Spaine "Spain," from Old French Espaigne (see Spaniard). Replaced Old English Speonisc. For Spanish Main see main. Spanish moss is attested from 1823. Spanish fly, the fabled aphrodisiac (ground-up cantharis blister-beetles), is attested from c.1600. Spanish-American War was so called in British press speculations early 1898, even before it began in April. For Spanish Inquisition (by c.1600), see Inquisition.
spank (v.): 1727, possibly imitative of the sound of spanking. Related: Spanked; spanking. The noun is from 1785.
spanking (adj.): 1660s, "very big or fine," later (especially of horses) "moving at a lively pace" (1738), perhaps from a Scandinavian source (cf. Danish spanke "to strut").
spanner (n.): 1630s, a tool for winding the spring of a wheel-lock firearm, from German Spanner, from spannen (see span (v.)). Meaning "wrench" is from 1790. Figurative phrase spanner in the works attested from 1921 (Wodehouse).
spar (n.1): "stout pole," c.1300, "rafter," from Middle Low German or Middle Dutch sparre, from Proto-Germanic *sparron (cf. Old English *spere "spear, lance," Old Norse sperra "rafter, beam"), from PIE root *sper- "spear, pole" (see spear). Nautical use dates from 1640. Also borrowed in Old French as esparre, which may have been the direct source of the English word.
spar (v): "to box," c.1400, "to strike or thrust," perhaps from Middle French esparer "to kick," from Italian sparare "to fling," from Latin ex- (see ex-) + parare "make ready, prepare," hence "ward off, parry" (see pare). Used in 17c. in reference to preliminary actions in a cock fight; figurative sense of "to dispute, bandy with words" is from 1690s. Extension to humans, with meaning "to engage in or practice boxing" is attested from 1755. Related: Sparred; sparring.
spar (n.2): "shiny mineral that splits easily," 1580s, from Low German Spar, from Middle Low German *spar, sper, cognate with Old English spær- in spærstan "gypsum."
sparagmos (n.): ritual death of a hero in tragedy or myth, 1949, from Greek sparagmos, literally "tearing, rending."
spare (adj.): "kept in reserve, not used," late 14c., from spare (v.). Old English had spær "spare, frugal." In reference to time, from mid-15c.; sense of "flimsy, thin" is recorded from 1540s. Spare part is attested from 1888.
spare (v.): Old English sparian "to refrain from harming, to allow to go free," from the source of Old English spær "sparing, frugal," from Proto-Germanic *sparaz (cf. Old Frisian sparia, Old Norse spara, Old High German sparon "to spare"). Meaning "to dispense from one's own stock" is recorded from early 13c. Related: Spared; sparing.
spare (n.): "extra thing or part," 1640s, from spare (v.). Middle English noun sense was "mercy, leniency" (early 14c.). Bowling sense of "a knocking down of all pins in two bowls" is attested from 1849, American English.
spare ribs: 1590s, from meaning "absence of fat" (see spare), or perhaps from Middle Low German ribbesper "spare ribs," from sper "spit," from Proto-Germanic *speru, from PIE *sper- "pole, spear," related to spar (n.1).
sparingly (adv.): mid-15c., from present participle of spare (v.) + -ly (2).
spark (n.): Old English spearca, from Proto-Germanic *spark- (cf. Middle Low German sparke, Middle Dutch spranke, not found in other Germanic languages). Electrical sense dates from 1748. Slang sense of "a gallant, a beau, a lover" (c.1600) is perhaps a figurative use, but also perhaps from cognate Old Norse sparkr "lively." Spark plug first recorded 1903 (sparking plug is from 1902); figurative sense of "one who initiates or is a driving force in some activity" is from 1941.
spark (v.): c.1300, from spark (n.). Slang meaning "stimulate, to trigger" first attested 1912. Related: Sparked; sparking.
sparkle (n.): early 14c., from sparkle (v.).
sparkle (v.): c.1200, frequentative verb form of Middle English sparke (see spark). Of wines, from early 15c. Related: Sparkled; sparkling.
sparkler (n.): in the hand-held fireworks sense, 1879, agent noun from sparkle (v.).
sparkly (adv.): 1922, from sparkle + -y (2). Related: Sparkliness.
sparrow (n.): small brownish-gray bird, Old English spearwa, from Proto-Germanic *sparwan (cf. Old Norse spörr, Old High German sparo, German Sperling, Gothic sparwa), from PIE *sper- (cf. Cornish frau "crow;" Old Prussian spurglis "sparrow;" Greek spergoulos "small field bird," psar "starling"). Sparrowhawk is attested from c.1400. Sparrowfarts (1886) was Cheshire slang for "very early morning."
sparse (adj.): 1727, from Latin sparsus "scattered," past participle of spargere "to scatter, spread," from PIE root *(s)pregh- "to jerk, scatter" (cf. Sanskrit parjanya- "rain, rain god," Avestan fra-sparega "branch, twig," literally "that which is jerked off a tree," Old Norse freknur "freckles," Swedish dialectal sprygg "brisk, active," Lithuanian sprogti "shoot, bud," Old Irish arg "a drop").
Sparta: said to be from Greek sparte "cord made from spartos," a type of broom. Perhaps the reference is to the cords laid as foundation markers for the city.
Spartacist: "German Bolshevik of November 1918 uprising," 1919, from German Spartakist, from Spartacus (d.71 B.C.E.), Thracian leader of Roman Servile War (73-71 B.C.E.), the name adopted 1916 as a pseudonym by Karl Liebknecht in his political tracts, and extended to the socialist revolutionary group he founded with Rosa Luxemburg and Franz Mehring.
Spartan: early 15c., "of or pertaining to the ancient Greek city of Sparta," from Sparta capital of Laconia, famed for severity of its social order, the frugality of its people, the valor of its army, and the brevity of its speech. Meaning "characterized by frugality or courage" is from 1640s.
spasm (n.): c.1400, from Old French spasme, from Latin spasmus "a spasm," from Greek spasmos "a spasm, convulsion," from span "draw up, tear away, contract violently, pull," from PIE *spe- "stretch." Figurative sense of "a sudden convulsion" (of emotion, politics, etc.) is attested from 1817.
spasm (v.): 1900, from spasm (n.). Related: Spasmed; spasming.
spasmodic (adj.): 1681, from Medieval Latin spasmodicus, from Greek spasmodes "of the nature of a spasm," from spasmos (see spasm) + -odes "like."
spastic (adj.): 1753, from Latin spasticus, from Greek spastikos "afflicted with spasms," literally "drawing, pulling," from span "draw up" (see spasm). The noun meaning "a person affected with spastic paralysis" is attested from 1896.
spat (n.1): "petty quarrel," 1804, American English, of unknown origin; perhaps somehow imitative (cf. spat "smack, slap," attested from 1823).
spat (n.2): "short gaiter covering the ankle," 1779, shortening of spatterdash "long gaiter to keep trousers or stockings from being spattered with mud" (1680s), from spatter and dash (v.).
spate (n.): early 15c., originally Scottish and northern English, "a sudden flood, especially one caused by heavy rains or a snowmelt," of unknown origin. Perhaps from Old French espoit "flood," from Dutch spuiten "to flow, spout;" related to spout. Figurative sense of "unusual quantity" is attested from 1610s.
spatial (adj.): 1847, from Latin spatium + adjectival suffix -al (1); formed in English as an adjective to space (n.), to go with temporal.
spatter (v.): 1570s (implied in spattering), possibly a frequentative verb from the stem of Dutch or Low German spatten "to spout, burst," of imitative origin. Related: Spattered.
spatula (n.): 1520s, from Latin spatula "broad piece, spatula," diminutive of spatha "broad, flat tool or weapon," from Greek spathe "broad blade" (see spade (n.1)). Erroneous form spattular is attested from c.1600.
spavin (n.): disease of the hock joint of a horse, early 15c., from Middle French espavain, perhaps from Frankish *sparwan "sparrow" (see sparrow), so called perhaps from comparison of the bird's awkward gait to that of a horse affected with spavin.
spawn (v.): early 15c., from Anglo-French espaundre, Old French espandre "to spread out, pour out," from Latin expandere (see expand). The notion is of a "spreading out" of fish eggs released in water. The meaning "to engender, give rise to" is attested from 1590s. Related: Spawned; spawning.
spawn (n.): early 15c., from spawn (v.); figurative sense of "brood, offspring" is from 1580s.
spay (v.): early 15c., "stab with a sword, kill," also "remove the ovaries of," from Anglo-French espeier "cut with a sword," from Middle French espeer, from Old French espee "sword" (French épée), from Latin spatha "broad, flat weapon or tool," from Greek spathe "broad blade" (see spade (n.1)).
spaz (n.): also spazz, by 1965, U.S. teen slang, apparently a derogatory shortening of spastic. Also used as a verb.
speak (v.): Old English specan, variant of sprecan "to speak" (class V strong verb; past tense spræc, past participle sprecen), from Proto-Germanic *sprekanan (cf. Old Saxon sprecan, Old Frisian spreka, Middle Dutch spreken, Old High German sprehhan, German sprechen "to speak," Old Norse spraki "rumor, report"), cognate with Latin spargere "to strew" (speech as a "scattering" of words; see sparse).

The -r- began to drop out in Late West Saxon and was gone by mid-12c., perhaps from influence of Danish spage "crackle," in a slang sense of "speak" (cf. crack in slang senses having to do with speech, e.g. wisecrack, cracker, all it's cracked up to be). Rare variant forms without -r- also are found in Middle Dutch (speken) and Old High German (spehhan).

Not the primary word for "to speak" in Old English (the "Beowulf" author prefers maþelian, from mæþel "assembly, council," from root of metan "to meet;" cf. Greek agoreuo "to speak," originally "speak in the assembly," from agora "assembly").
speakeasy (n.): "unlicensed saloon," 1889 (in New York "Voice"), from speak + easy; so called from the practice of speaking quietly about such a place in public, or when inside it, so as not to alert the police and neighbors. The word gained wide currency in U.S. during Prohibition (1920-1932). In early 19c. Irish and British dialect, a speak softly shop meant "smuggler's den."
speaker (n.): c.1300, "one who speaks," agent noun from speak (v.). First applied to "person who presides over an assembly" c.1400, from Anglo-French (late 14c.). In reference to the English Parliament, Sir Thomas de Hungerford apparently was the first.