Online Etymology Dictionary

soiree (n.): "an evening party," 1793, from French soirée, from soir "evening," from Old French soir "evening, night" (10c.), from Latin sero (adv.) "late, at a late hour," from serum "late hour," neuter of serus "late," from PIE *se-ro-, suffixed form of root *se- (2) "long, late" (source also of Sanskrit sayam "in the evening," Lithuanian sietuva "deep place in a river," Old English sið "after," German seit "since," Gothic seiþus "late," Middle Irish sith, Middle Breton hir "long"). For suffix, compare journey.
sojourn (v.): late 13c., "stay temporarily, reside for a time; visit;" also "reside permanently, dwell;" from Old French sojorner "stay or dwell for a time," from Vulgar Latin *subdiurnare "to spend the day" (source also of Italian soggiornare), from Latin sub- "under, until" (see sub-) + diurnare "to last long," from diurnus "of a day," from diurnum "day" (see diurnal). Modern French séjourner formed via vowel dissimilation. Related: Sojourned; sojourning.
sojourn (n.): mid-13c., "temporary stay, visit," from Anglo-French sojorn, variant of Old French sejorn, from sejorner "stay or dwell for a time" (see sojourn (v.)).
sojourner (n.): "temporary resident," 15c., agent noun from sojourn (v.).
soke (n.): "right of jurisdiction," Old English socn "jurisdiction, prosecution," literally "seeking," from Proto-Germanic *sokniz, from PIE *sag-ni-, from root *sag- "to seek out" (see seek). Related: Sokeman; sokemanry.
Sol (n.): "the sun personified," mid-15c. (also in Old English), from Latin sol "the sun, sunlight," from PIE *s(e)wol-, variant of root *saewel- "the sun" (source also of Sanskrit suryah, Avestan hvar "sun, light, heavens;" Greek helios; Lithuanian saule; Old Church Slavonic slunice; Gothic sauil, Old English sol "sun," swegl "sky, heavens, the sun;" Welsh haul, Old Cornish heuul, Breton heol "sun;" Old Irish suil "eye").

The PIE element -*el- in the root originally was a suffix and had an alternative form -*en-, yielding *s(u)wen-, source of English sun (n.). French soleil (10c.) is from Vulgar Latin *soliculus, diminutive of sol; in Vulgar Latin diminutives had the full meaning of their principal words.
sol-fa (n.): "syllables used in solmization taken collectively," 1540s, from Italian, from Medieval Latin sol and fa, two notes of the musical scale (see gamut). As a verb from 1560s; compare solfeggio "use the sol-fa system" (1774), from Italian solfeggiare.
solace (n.): "comfort in grief, consolation," late 13c., from Old French solaz "pleasure, entertainment, enjoyment; solace, comfort," from Latin solacium "a soothing, assuaging; comfort, consolation," from solatus, past participle of solari "to console, soothe," from PIE *sol-a-, suffixed form of root *sele- "of good mood; to favor" (source also of Old English gesælig "happy;" see silly). Adjectival form solacious is attested 16c.-17c.
solace (v.): "comfort, console in grief," late 13c.; also in Middle English "entertain, amuse, please," from Old French solacier "comfort, console" (often with a sexual connotation) and directly from Medieval Latin solatiare "give solace, console" (source also of Spanish solazar, Italian sollazzare), from Latin solacium (see solace (n.)). Related: Solaced; solacing.
solar (adj.): mid-15c., "pertaining to the sun," from Latin solaris "of the sun," from sol "sun" (see sol). Meaning "living room on an upper story" is from Old English, from Latin solarium (see solarium). Old English had sunlic "solar."

Astrological sense from 1620s. Meaning "operated by means of the sun" is from 1740; solar power is attested from 1915, solar cell from 1955, solar panel from 1964. Solar system is attested from c. 1704; solar wind is from 1958. Solar plexus (1771) "complex of nerves in the pit of the stomach," apparently so called from its central position in the body (see plexus).
solarium (n.): 1891, "part of a house arranged to receive the sun's rays," earlier "sundial" (1842), from Latin solarium "sundial," also "a flat housetop," literally "that which is exposed to the sun," from sol "sun" (see sol).
sold: past tense and past participle of sell (v.); from Old English salde.
solder (v.): mid-14c., sawd "mend by soldering," from solder (n.). Modern form is a re-Latinization from early 15c. Related: Soldered; soldering.
solder (n.): early 14c., soudur, from Old French soldure, soudeure, from souder, originally solder, "to consolidate, close, fasten together, join with solder" (13c.), from Latin solidare "to make solid," from solidus "solid" (see solid (adj.)).

Modern form in English is a re-Latinization from early 15c. The loss of Latin -l- in that position on the way to Old French is regular, as poudre from pulverem, cou from collum, chaud from calidus. The -l- typically is sounded in British English but not in American, according to OED, but Fowler wrote that solder without the "l" was "The only pronunciation I have ever heard, except from the half-educated to whom spelling is a final court of appeal ..." and was baffled by the OED's statement that it was American. Related: Soldered; soldering. The noun is first attested late 14c.
soldier (n.): c. 1300, souder, from Old French soudier, soldier "one who serves in the army for pay," from Medieval Latin soldarius "a soldier" (source also of Spanish soldado, Italian soldato), literally "one having pay," from Late Latin soldum, extended sense of accusative of Latin solidus, name of a Roman gold coin (see solidus).

The -l- has been regular in English since mid-14c., in imitation of Latin. Willie and Joe always say sojer in the Bill Mauldin cartoons, and this seems to mirror 16c.-17c. spellings sojar, soger, sojour. Modern French soldat is borrowed from Italian and displaced the older French word; one of many military (and other) terms picked up during the Italian Wars in early 16c.; such as alert, arsenal, colonel, infantrie, sentinel.

Old slang names for military men circa early 19c. include mud-crusher "infantryman," cat-shooter "volunteer," fly-slicer "cavalryman," jolly gravel-grinder "marine."
soldier (v.): "to serve as a soldier," 1640s, from soldier (n.). Related: Soldiered; soldiering. To soldier on "persist doggedly" is attested from 1954.
soldiery (n.): 1560s, from Middle French souderie or else a native formation from soldier + -y (1).
sole (n.1): "bottom of the foot" ("technically, the planta, corresponding to the palm of the hand," Century Dictionary), early 14c., from Old French sole, from Vulgar Latin *sola, from Latin solea "sandal, bottom of a shoe; a flatfish," from solum "bottom, ground, foundation, lowest point of a thing" (hence "sole of the foot"), a word of uncertain origin. In English, the meaning "bottom of a shoe or boot" is from late 14c.
sole (adj.): "single, alone, having no husband or wife; one and only, singular, unique," late 14c., from Old French soul "only, alone, just," from Latin solus "alone, only, single, sole; forsaken; extraordinary," of unknown origin, perhaps related to se "oneself," from PIE reflexive root *swo- (see so).
sole (n.2): common European flatfish, mid-13c., from Old French sole, from Latin solea "a kind of flatfish," originally "sandal" (see sole (n.1)); so called from resemblance of the fish to a flat shoe.
sole (v.): "furnish (a shoe) with a sole," 1560s, from sole (n.1). Related: Soled; soling.
solecism (n.): "gross grammatical error;" loosely "any absurdity or incongruity," 1570s, from Middle French solécisme (16c.), from Latin soloecismus "mistake in speaking or writing," from Greek soloikismos "to speak (Greek) incorrectly," from soloikos "ungrammatical utterance," properly "a speaking like the people of Soloi," an Athenian colony in Cilicia (modern Mezitli in Turkey), whose dialect the Athenians considered barbarous. Related: Solecistic.
solely (adv.): late 15c., from sole (adj.) + -ly (2).
solemn (adj.): mid-14c., "performed with due religious ceremony or reverence, sacred, devoted to religious observances," also, of a vow, etc., "made under religious sanction, binding," from Old French solempne (12c., Modern French solennel) and directly from Latin sollemnis "annual, established, religiously fixed, formal, ceremonial, traditional," perhaps related to sollus "whole" (see safe (adj.)).

"The explanation that Latin sollemnis was formed from sollus whole + annus year is not considered valid" [Barnhart], but some assimilation via folk-etymology is possible. In Middle English also "famous, important; imposing, grand," hence Chaucer's friar, a ful solempne man. Meaning "marked by seriousness or earnestness" is from late 14c.; sense of "fitted to inspire devout reflection" is from c. 1400. Related: Solemnly.
solemnity (n.): c. 1300, "observance of ceremony," from Old French solemnite, solempnete "celebration, high festival, church ceremony" and directly from Latin solemnitatem (nominative solemnitas) "a solemnity," from sollemnis (see solemn). Meaning "state of being solemn" is from 1712. Related: Solemnities.
solemnization (n.): mid-15c., "act of celebrating," from Old French solemnisation, solempnisation, or directly from Medieval Latin solempnizationem (nominative solempnizatio), from Latin sollemnis (see solemn).
solemnize (v.): late 14c., "honor by ceremonies," from Old French solemnisier, from Medieval Latin solemnizare, from Latin solemnis (see solemn). Meaning "render solemn" is from 1726. Related: Solemnized; solemnizing.
solenoid (n.): "coil of insulated wire carrying an electrical current and having magnetic properties," 1827, from French solénoïde, from Greek solenoeides "pipe-shaped," from solen "pipe, channel" + comb. form of eidos "form, shape" (see -oid). Related: Solenoidal.
soleus (n.): muscle of the calf of the leg, 1670s, Modern Latin, from Latin solea "sole" (see sole (n.1)). So called for its flatness.
solfege (adj.): 1912, from solfeggio (1774), from Italian solfeggio, from sol-fa, representing musical notes (see sol-fa).
solicit (v.): early 15c., "to disturb, trouble," from Middle French soliciter (14c.), from Latin sollicitare "to disturb, rouse, trouble, harass; stimulate, provoke," from sollicitus "agitated," from sollus "whole, entire" + citus "aroused," past participle of ciere "shake, excite, set in motion" (see cite). Related: Solicited; soliciting.

Meaning "entreat, petition" is from 1520s. Meaning "to further (business affairs)" evolved mid-15c. from Middle French sense of "manage affairs." The sexual sense (often in reference to prostitutes) is attested from 1710, probably from a merger of the business sense and an earlier sense of "to court or beg the favor of" (a woman), attested from 1590s.
solicitate (v.): 1540s, from Latin solicitatus, past participle of sollicitare (see solicit). Related: Solicitated; solicitating.
solicitation (n.): late 15c., "management," from Middle French solicitation and directly from Latin solicitationem (nominative solicitatio) "vexation, disturbance, instigation," noun of action from past participle stem of solicitare (see solicit). Meaning "action of soliciting" is from 1520s. Specific sexual sense is from c. 1600.
solicitor (n.): early 15c., "one who urges," from Middle French soliciteur, from soliciter (see solicit). Meaning "one who conducts matters on behalf of another" is from early 15c. As a name for a specific class of legal practitioners in Britain, it is attested from 1570s. Both the fem. forms, solicitress (1630s) and solicitrix (1610s), have been in the sexual sense, but the latter seems more common in non-pejorative use.
solicitous (adj.): 1560s, from Latin sollicitus "restless, uneasy, careful, full of anxiety" (see solicit). Related: Solicitously; solicitousness.
solicitude (n.): early 15c., from Middle French solicitude (Modern French sollicitude), and directly from Latin sollicitudinem (nominative solicitudo) "anxiety, uneasiness of mind," noun of state from past participle stem of solicitare (see solicit).
solid (adj.): late 14c., "not empty or hollow," from Old French solide "firm, dense, compact," from Latin solidus "firm, whole, undivided, entire," figuratively "sound, trustworthy, genuine," from PIE *sol-ido-, suffixed form of root *sol- "whole" (source also of Greek holos "whole," Latin salus "health," salvus "safe;" see safe (adj.)).

Meaning "firm, hard, compact" is from 1530s. Meaning "entirely of the same stuff" is from 1710. Of qualities, "well-established, considerable" c. 1600. As a mere intensifier, 1830. Slang sense of "wonderful, remarkable" first attested 1920 among jazz musicians. As an adverb, "solidly, completely," 1650s. Solid South in U.S. political history is attested from 1858. Solid state as a term in physics is recorded from 1953; meaning "employing printed circuits and solid transistors" (as opposed to wires and vacuum tubes) is from 1959. Related: Solidly.
solid (n.): late 14c., "three-dimensional figure," from solid (adj.). Meaning "a solid substance" is from 1690s. Compare also solidus; Latin solidus (adj.) was used as a noun meaning "an entire sum; a solid body."
solidarity (n.): 1829, from French solidarité "communion of interests and responsibilities, mutual responsibility," a coinage of the "Encyclopédie" (1765), from solidaire "interdependent, complete, entire," from solide (see solid (adj.)). With a capital S-, the name of an independent trade union movement in Poland, formed September 1980, from Polish Solidarność.
solidary (adj.): 1818, from French solidaire (16c.), from solide (see solid (adj.)).
solidification (n.): 1800; noun of action from solidify; perhaps from French solidification. Earlier was solidation (1540s).
solidify (v.): 1799 (transitive); 1837 (intransitive), from French solidifier, from Old French solide (see solid (adj.)) + -fier (see -fy). Related: Solidified; solidifying.
solidity (n.): late 14c., from Middle French solidité or directly from Latin soliditatem (nominative soliditas), from solidus (see solid (adj.)).
solidly (adv.): 1610s, "firmly, securely," from solid (adj.) + -ly (2). Meaning "unanimously" is from 1865, American English.
solidus (n.): late 14c., plural solidi, used of both English shilling and Roman gold coin, from Late Latin solidus, an imperial Roman coin (worth about 25 denarii), from nummus solidus, literally "solid coin," properly a coin of thick or solid metal, not of thin plate (see solid (adj.)).
solifidian (n.): "one who believes in salvation by faith alone" (based on Luther's translation of Rom. iii:28), 1590s, Reformation coinage from Latin solus "alone" (see sole (adj.)) + fides "faith" (see faith). As an adjective from c. 1600. Related: Solifidianism
soliloquize (v.): 1759, from soliloquy + -ize. Related: Soliloquized; soliloquizing.
soliloquy (n.): 1610s, from Late Latin soliloquium "a talking to oneself," from Latin solus "alone" (see sole (adj.)) + loqui "speak" (see locution). Also used in translation of Latin "Liber Soliloquiorum," a treatise by Augustine, who is said to have coined the word, on analogy of Greek monologia (see monologue). Related: Soliloquent.
solipsism (n.): 1871, coined from Latin solus "alone" (see sole (adj.)) + ipse "self." The view or theory that self is the only object of real knowledge or the only thing that is real. "The identification of one's self with the Absolute is not generally intended, but the denial of there being really anybody else" [Century Dictionary].
solipsistic (adj.): 1882, from solipsism + -istic. Related: Solipsist; solipsistically.