Online Etymology Dictionary

citadel (n.): 1580s, "fortress commanding a city," from Middle French citadelle (15c.), from Italian cittadella, diminutive of Old Italian cittade "city" (Modern Italian citta), from Latin civitatem (nominative civitas; also source of Portuguese citadella, Spanish ciuadela; see city).
citation (n.): c. 1300, "summons, written notice to appear," from Old French citation or directly from Latin citationem (nominative citatio) "a command," noun of action from past participle stem of citare "to summon, urge, call; put in sudden motion, call forward; rouse, excite" (see cite). Meaning "passage cited, quotation" is from 1540s. From 1918 as "a mention in an official dispatch."
cite (v.): mid-15c., "to summon," from Old French citer "to summon" (14c.), from Latin citare "to summon, urge, call; put in sudden motion, call forward; rouse, excite," frequentative of ciere "to move, set in motion, stir, rouse, call, invite" from PIE root *keie- "to set in motion, to move to and fro" (source also of Sanskrit cyavate "stirs himself, goes;" Greek kinein "to move, set in motion; change, stir up," kinymai "move myself;" Gothic haitan "call, be called;" Old English hatan "command, call"). Sense of "calling forth a passage of writing" is first attested 1530s. Related: Cited; citing.
citified (adj.): 1819, American English, from city + past participle ending from words in -fy.
citify (v.): 1865, probably a back formation from citified. Related: Citifying.
citizen (n.): early 14c., "inhabitant of a city," from Anglo-French citezein (spelling subsequently altered, probably by influence of denizen), from Old French citeien "city-dweller, town-dweller, citizen" (12c., Modern French citoyen), from cite (see city) + -ain (see -ian). Replaced Old English burhsittend and ceasterware. Sense of "inhabitant of a country" is late 14c. Citizen's arrest recorded from 1941; citizen's band (radio) from 1947. Citizen of the world (late 15c.) translates Greek kosmopolites.
citizenry (n.): "citizens collectively," 1795, from citizen + -ry.
citizenship (n.): "status, rights, privileges, and responsibilities of a citizen," 1610s, from citizen + -ship.
citric (adj.): 1800, from Modern Latin citricum (in acidum citricum "citric acid," discovered by Scheele in 1784; see citrus + -ic. The classical adjective was citreus.
citrine (adj.): lemon-colored, late 14c., from French citrin, from Latin citrus (see citrus). From 1879 as a color name.
citron (n.): late 14c., also citrine (early 15c.), from Old French citron "citron, lemon" (14c.), possibly from Old Provençal citron, from Latin citrus and influenced by lemon; or else from augmentative of Latin *citrum, related to citrus "citron tree," citreum (malum) "citron" (see citrus).
citronella (n.): 1858 in reference to a type of fragrant grass, and especially to the oil it yields, from French citronelle "lemon liquor," from citron (see citrus). Originally an Asiatic grass used in perfumes, later applied to a substance found in lemon oil, etc.
citrus (adj.): 1825, from Modern Latin genus name, from Latin citrus "citron tree," name of an African tree with aromatic wood and lemon-like fruit, the first citrus fruit to become available in the West. The name, like the tree, is probably of Asiatic origin [OED]. But Klein traces it to Greek kedros "cedar," and writes that the change of dr into tr shows that the word came from Greek into Latin through the medium of the Etruscans. As a noun, "tree of the genus Citrus," from 1885.
city (n.): early 13c., in medieval usage a cathedral town, but originally "any settlement," regardless of size (distinction from town is 14c., though in English it always seems to have ranked above borough), from Old French cite "town, city" (10c., Modern French cité), from earlier citet, from Latin civitatem (nominative civitas; in Late Latin sometimes citatem) originally "citizenship, condition or rights of a citizen, membership in the community," later "community of citizens, state, commonwealth" (used, for instance of the Gaulish tribes), from civis "townsman," from PIE root *kei- "to lie; bed, couch; homestead; beloved, dear" (see cemetery).

The sense has been transferred from the inhabitants to the place. The Latin word for "city" was urbs, but a resident was civis. Civitas seems to have replaced urbs as Rome (the ultimate urbs) lost its prestige. Loss of Latin -v- is regular in French in some situations (compare alleger from alleviare; neige from nivea; jeune from juvenis. A different sound evolution from the Latin word yielded Italian citta, Catalan ciutat, Spanish ciudad, Portuguese cidade.

Replaced Old English burh (see borough). London is the city from 1550s. As an adjective from c. 1300. City hall first recorded 1670s to fight city hall is 1913, American English; city slicker first recorded 1916 (see slick); both American English. City limits is from 1825. The newspaper city desk attested from 1878. Inner city first attested 1968. City state (also city-state) is attested from 1877.
civet (n.): 1530s, from Middle French civette (15c.), ultimately (with Italian zibetto, Medieval Latin zibethum, Medieval Greek zapetion) via lost intermediate forms from Arabic zabad "civet," said to be related to zabad "foam, froth," zubd "cream."
civic (adj.): 1540s, originally mostly in civic crown (Latin corona civica), a chaplet of oak leaves awarded to one who saved the life of a fellow citizen in battle, from Latin civicus "of a citizen," adjectival derivation of civis "townsman" (see city). Sense of "having to do with citizens" is from 1790.
civics (n.): "study of the rights and responsibilities of a citizen," 1886, originally American English, from civic, by analogy with politics (see -ics).
civil (adj.): late 14c., "relating to civil law or life; pertaining to the internal affairs of a state," from Old French civil "civil, relating to civil law" (13c.) and directly from Latin civilis "relating to a citizen, relating to public life, befitting a citizen," hence by extension "popular, affable, courteous;" alternative adjectival derivation of civis "townsman" (see city).

The sense of "polite" was in classical Latin, from the courteous manners of citizens, as opposed to those of soldiers. But English did not pick up this nuance of the word until late 16c. "Courteous is thus more commonly said of superiors, civil of inferiors, since it implies or suggests the possibility of incivility or rudeness" [OED]. Civil case (as opposed to criminal) is recorded from 1610s. Civil liberty is by 1640s. Civil service is from 1772, originally in reference to the East India Company.
civil disobedience (n.): coined 1866 by Thoreau as title of an essay originally published (1849) as "Resistance to Civil Government."
civil rights (n.): 1721, American English; specifically of black U.S. citizens from 1866.
civil service (n.): c. 1785, originally in reference to non-military staff of the East India Company. Civil servant is from 1800.
civil union (n.): by 2000, the usual U.S. term for legally recognized same-sex unions short of marriage.
civil war (n.): "battles among fellow citizens or within a community," from civil in a sense of "occurring among fellow citizens" attested from late 14c. in batayle ciuile "civil battle," etc. The exact phrase civil war is attested from late 15c. (the Latin phrase was bella civicus). An Old English word for it was ingewinn. Ancient Greek had polemos epidemios.

Early use typically was in reference to ancient Rome. Later, in England, to the struggle between Parliament and Charles I (1641-1651); in U.S., to the War of Secession (1861-1865), an application often decried as wholly inaccurate but in use (among other names) in the North during the war and boosted by the use of the term in the popular "Battles and Leaders of the Civil War" series published 1884-87 in "Century Magazine."
"The war between the States," which a good many Southerners prefer, is both bookish and inexact. "Civil war" is an utter misnomer. It was used and is still used by courteous people, the same people who are careful to say "Federal" and "Confederate." "War of the rebellion," which begs the very question at issue, has become the official designation of the struggle, but has found no acceptance with the vanquished. To this day no Southerner uses it except by way of quotation .... "The war of secession" is still used a good deal in foreign books, but it has no popular hold. "The war," without any further qualification, served the turn of Thucydides and Aristophanes for the Peloponnesian war. It will serve ours, let it be hoped, for some time to come. [Basil L. Gildersleeve, "The Creed of the Old South," 1915]
civilian (n.): late 14c., "judge or authority on civil law," from Old French civilien "of the civil law," created from Latin civilis "relating to a citizen, relating to public life, befitting a citizen; popular, affable, courteous" (see civil). Sense of "non-military person" is attested by 1819 (earlier in this sense was civilian, attested from c. 1600 as "non-soldier"). The adjective is from 1640s.
civilisation (n.): chiefly British English spelling of civilization. Also see -ize.
civility (n.): late 14c., "status of a citizen," from Old French civilite (14c.), from Latin civitatem (nominative civitas) "the art of governing; courteousness," from cvilis "relating to a citizen, relating to public life, befitting a citizen; popular, affable, courteous" (see civil). Later especially "good citizenship" (1530s). Also "state of being civilized" (1540s); "behavior proper to civilized persons" (1560s).
civilization (n.): 1704, "law which makes a criminal process civil," from civilize + -ation. Sense of "civilized condition" first recorded 1772, probably from French civilisation, to be an opposite to barbarity and a distinct word from civility. Sense of a particular human society in a civilized condition, considered as a whole over time, is from 1857. Related: Civilizational.
civilize (v.): c. 1600, "to bring out of barbarism," from French civiliser, verb from Old French civil (adj.), from Latin civilis "relating to a citizen, relating to public life, befitting a citizen; popular, affable, courteous" (see civil). Meaning "become civilized" is from 1868. Related: Civilized; civilizing.
civilized (adj.): 1610s, past participle adjective from civilize.
civilly (adv.): 1550s, "with reference to citizenship or civil matters," also "in a well-bred manner;" from civil + -ly (2).
civvy (n.): 1889, civvies, short for civilian clothes (see civilian (adj.)); in reference to civilian clothes of military men.
clabber (n.): "mud," 1824, from Irish and Gaelic clabar "mud." Also often short for bonnyclabber.
clachan (n.): "small village" (Scottish and Irish), early 15c., from Gaelic clach (plural clachan) "stone."
clack (v.): mid-13c., not in Old English, from Old Norse klaka "to chatter," of echoic origin; compare Dutch klakken "to clack, crack," Old High German kleken, French claquer "to clap, crack (see claque). Related: Clacked; clacking.
clack (n.): mid-15c., from clack (v.).
clad (adj.): "clothed," c. 1300, mid-13c., from clad, alternative past tense and past participle of clothe. Old English had geclæþd, past participle of clæþan.
claddagh: in Claddagh ring (Irish fáinne Chladach), from village of Claddagh, County Gallway. The village name is literally "stony beach."
clade (n.): "group of organisms evolved from a common ancestor," 1957, from Greek klados "young branch, offshoot of a plant, shoot broken off," from PIE *kele-, possibly from root *kel- (1) "to strike, cut" (see holt).
cladism (n.): 1966, from clade + -ism. Related: Cladist.
cladistic (adj.): 1960, from clade + -istic. Related: Cladistics "systematic classification of life forms" (1965; see -ics).
claim (v.): c. 1300, "to call, call out; to ask or demand by virtue of right or authority," from accented stem of Old French clamer "to call, name, describe; claim; complain; declare," from Latin clamare "to cry out, shout, proclaim," from PIE *kele- (2) "to shout," imitative (compare Sanskrit usakala "cock," literally "dawn-calling;" Latin calare "to announce solemnly, call out;" Middle Irish cailech "cock;" Greek kalein "to call," kelados "noise," kledon "report, fame;" Old High German halan "to call;" Old English hlowan "to low, make a noise like a cow;" Lithuanian kalba "language"). Related: Claimed; claiming.

Meaning "to maintain as true" is from 1864; specific sense "to make a claim" (on an insurance company) is from 1897. Claim properly should not stray too far from its true meaning of "to demand recognition of a right."
claim (n.): early 14c., "a demand of a right; right of claiming," from Old French claime "claim, complaint," from clamer (see claim (v.)). Meaning "thing claimed or demanded" is from 1792; specifically "piece of land allotted and taken" (chiefly U.S. and Australia, in reference to mining) is from 1851. Insurance sense is from 1878.
claimant (n.): 1747, from claim (v.), on model of appellant, defendant, etc., or from French noun use of present participle of clamer.
clair-de-lune (n.): 1877, French, literally "moonlight," also used as "color of moonlight." See clear (adj.) + Luna.
clairaudience (n.): 1864, formed on model of clairvoyance (with French clair; see clear (adj.)) + audience.
Claire: fem. proper name, from French claire, fem. of clair literally "light, bright," from Latin clarus "clear, bright, distinct" (see clear (adj.); also compare Clara).
clairvoyance (n.): "paranormal gift of seeing things out of sight," 1837, from special use of French clairvoyance (Old French clerveans, 13c.) "quickness of understanding, sagacity, penetration," from clairvoyant (see clairvoyant). A secondary sense in French is the main sense in English.
clairvoyant (adj.): "having psychic gifts," 1837, earlier "having insight" (1670s), from special use of French clairvoyant "clear-sighted, discerning, judicious" (13c.), from clair (see clear (adj.)) + voyant "seeing," present participle of voir, from Latin videre "to see" (see vision).
clairvoyant (n.): 1834 in the psychic sense; see clairvoyant (adj.). Earlier it was used in the sense "clear-sighted person" (1794). Fem. form was Clairvoyante.
clam (n.): bivalve mollusk, c. 1500, in clam-shell, originally Scottish, apparently a particular use from Middle English clam "pincers, vice, clamp" (late 14c.), from Old English clamm "bond, fetter, grip, grasp," from Proto-Germanic *klam- "to press or squeeze together" (source also of Old High German klamma "cramp, fetter, constriction," German Klamm "a constriction"). If this is right then the original reference is to the shell. Clam-chowder attested from 1822. To be happy as a clam is from 1833, but the earliest uses do not elaborate on the notion behind it, unless it be self-containment.