Online Etymology Dictionary

cogency (n.): 1680s, from cogent + -cy.
cogenial (adj.): 1774, variant of congenial.
cogent (adj.): 1650s, from French cogent "necessary, urgent" (14c.), from Latin cogentem (nominative cogens), present participle of cogere "to curdle; to compel; to collect," literally "to drive together," from com- "together" (see co-) + agere "to drive" (see act (n.)).
cogitate (v.): late 16c., from Latin cogitatus, past participle of cogitare "to think" (see cogitation). Related: Cogitated; cogitating.
cogitation (n.): c. 1200, "thought, idea, notion," from Old French cogitacion "thought, consideration, reflection," from Latin cogitationem (nominative cogitatio), noun of action from past participle stem of cogitare "to think, reflect, consider, turn over in the mind," apparently from co-agitare, from com- "together" (see co-) + agitare, here in a sense of "to turn over in the mind," literally "to put in constant motion, drive, impel," frequentative of agere "to move, drive" (see act (v.)).
cogitative (adj.): late 15c., from Old French cogitatif (14c.), from Medieval Latin cogitativus, from Latin cogitare "to think" (see cogitation).
cognac (n.): 1590s, Coniacke, "wine produced in Cognac," the region in western France. The sense of "brandy" is 1755, shortened from 17c. cognac brandy, which was distilled from cognac wine. The place name is from Medieval Latin Comniacum, from the personal name Cominius and the Gallo-Roman suffix -acum.
cognate (adj.): 1640s, from Latin cognatus "of common descent," from com- "together" (see co-) + gnatus, past participle of gnasci, older form of nasci "to be born" (see genus). Words that are cognates are cousins, not siblings. As a noun, from 1754.
cognisance (n.): alternative spelling of cognizance (q.v.); also see -ize.
cognisant (adj.): alternative spelling of cognizant (q.v.); also see -ize.
cognition (n.): mid-15c., "ability to comprehend," from Latin cognitionem (nominative cognitio) "a getting to know, acquaintance, knowledge," noun of action from past participle stem of cognoscere "to get to know, recognize" (see cognizance).
cognitive (adv.): 1580s, from Latin cognit-, past participle stem of cognoscere "to get to know, recognize" (see cognizance) + -ive. Taken over by psychologists and sociologists after c. 1940. Related: Cognitively.
cognitive dissonance (n.): 1957, developed and apparently coined by U.S. social psychologist Leon Festinger (1919-1989).
cognizable (adj.): 1670s, "capable of being known," also "liable to be tried in a given court or jurisdiction," from stem of cognizance + -able.
cognizance (n.): mid-14c., from Anglo-French conysance "recognition," later, "knowledge," from Old French conoissance "acquaintance, recognition; knowledge, wisdom" (Modern French connaissance), from past participle of conoistre "to know," from Latin cognoscere "to get to know, recognize," from com- "together" (see co-) + gnoscere "to know" (see notice (n.)). The -g- was restored in English spelling 15c. and has gradually affected the pronunciation, which was always "con-." The old pronunciation lingered longest in legal use.
cognizant (adj.): 1820, back-formation from cognizance.
cognize (v.): 1650s, back-formation from cognizance. Related: Cognized; cognizing.
cognomen (n.): 1809, from Latin com- "with" (see co-) + (g)nomen "name" (see name (n.)). Third or family name of a Roman citizen (Caius Julius Cæsar).
cognoscence (n.): mid-15c., from Latin cognoscere "to get to know, recognize" (see cognizance).
cognoscente (n.): "connoisseur," 1778, from Italian cognoscente, Latinized from conoscente "connoisseur," literally "knowing man," from Latin cognoscentum (nominative cognoscens), present participle of cognoscere "to get to know, recognize" (see cognizance).
cognoscenti (n.): plural of cognoscente (q.v.).
cohabit (v.): euphemism since 1530s to describe a couple living together without benefit of marriage; back-formation from cohabitation. Related: Cohabited; cohabiting.
cohabitate (v.): 1630s, from Late Latin cohabitatus, past participle of cohabitare (see cohabitation). Related: Cohabitated; cohabitating.
cohabitation (n.): mid-15c., "action or state of living together (especially as husband and wife)," from Middle French cohabitation (Old French cohabitacion "cohabitation, sexual intercourse"), from Late Latin cohabitationem (nominative cohabitatio), noun of action from past participle stem of cohabitare "to dwell together," from co- "with, together" (see co-) + habitare "to live, inhabit, dwell," frequentative of habere "to have, to hold, possess" (see habit (n.)).
Cohen: Jewish surname indicating priestly descent, from Hebrew kohen "priest," from base of kihen "he acted as priest," related to Arabic kahana "he divined, prophesied."
cohere (v.): 1590s, from Latin cohaerere "to cleave together," in transferred use, "be coherent or consistent," from com- "together" (see co-) + haerere "to stick" (see hesitation). Related: Cohered; cohering.
coherence (n.): late 16c., from Middle French cohérence (16c.), from Latin cohaerentia, noun of state from cohaerentem (see coherent). Related: Coherency.
coherent (adj.): 1550s, from Middle French cohérent (16c.), from Latin cohaerentem (nominative cohaerens), present participle of cohaerere "cohere," from com- "together" (see co-) + haerere "to stick" (see hesitation).
cohesion (n.): 1670s, from French cohésion, from Latin cohaesionem (nominative cohaesio) "a sticking together," noun of action from past participle stem of cohaerere "to stick together" (see cohere).
cohesive (adj.): c. 1730 (implied in cohesiveness), from Latin cohaes-, past participle stem of cohaerere (see cohere) + -ive. Related: Cohesively.
cohort (n.): early 15c., "company of soldiers," from Middle French cohorte (14c.) and directly from Latin cohortem (nominative cohors) "enclosure," meaning extended to "infantry company" in Roman army (a tenth part of a legion) through notion of "enclosed group, retinue," from com- "with" (see co-) + root akin to hortus "garden," from PIE *ghr-ti-, from root *gher- (1) "to grasp, enclose" (see yard (n.1)). Sense of "accomplice" is first recorded 1952, American English, from meaning "group united in common cause" (1719).
coif (n.): late 13c., "close-fitting cap," from Old French coife "skull-cap, cap worn under a helmet, headgear" (12c., Modern French coiffe), from Late Latin coifa "a cap, hood" (source of Italian cuffia, Spanish cofia, escofia), of West Germanic origin (compare Old High German kupphia, Middle High German kupfe "cap").
coif (v.): mid-15c., "to cover with a cap," from Middle French coiffer, from Old French coife (see coif (n.)); sense of "to arrange the hair" is attested in English from 1835. Related: Coifed; coifing.
coiffeur (n.): 1847, from French coiffeur "hairdresser," from coiffer "to dress hair," from Old French coife, originally, "inner part of the helmet" (see coif (n.)). A woman hairdresser would be properly a coiffeuse.
coiffure (n.): "style or fashion of wearing the hair," 1630s, from French coiffure, from coiffer (see coiffeur).
coign (n.): archaic spelling of quoin (q.v.), surviving only in Shakespeare's coign of vantage ("Macbeth" I.vi.), popularized by Sir Walter Scott, properly "a projecting corner" (for observation).
coil (v.): "to wind," 1610s, from Middle French coillir "to gather, pick," from Latin colligere "to gather together" (see collect). Meaning specialized perhaps in nautical usage. Related: Coiled; coiling.
coil (n.): 1620s, from coil (v.). Related: Coils.
coin (n.): c. 1300, "a wedge," from Old French coing (12c.) "a wedge; stamp; piece of money; corner, angle," from Latin cuneus "a wedge." The die for stamping metal was wedge-shaped, and the English word came to mean "thing stamped, a piece of money" by late 14c. (a sense that already had developed in French). Compare quoin, which split off from this word 16c. Modern French coin is "corner, angle, nook." Coins were first struck in western Asia Minor in 7c. B.C.E.; Greek tradition and Herodotus credit the Lydians with being first to make and use coins of silver and gold.
coin (v.): "to coin money," mid-14c., from coin (n.). Related: Coined; coining. To coin a phrase is late 16c. A Middle English word for minter was coin-smiter.
coinage (n.): late 14c., "currency, money," from Old French coignage, from coignier "to coin" (see coin (n.)). Meaning "act or process of coining money" is from early 15c.; sense "deliberate formation of a new word" is from 1690s, from a general sense of "something invented" (c. 1600).
coincide (v.): 1705, "be identical in substance or nature," but from 1640s as a verb in English in Latin form, "occupy the same space, agree in position," from Medieval Latin coincidere (used in astrology), literally "to fall upon together," from Latin com- "together" (see co-) + incidere "to fall upon" (in- "upon" + cadere "to fall;" see case (n.1)). From 1809 as "occur at the same time." Related: Coincided; coinciding.
coincidence (n.): c. 1600, "exact correspondence in substance or nature," from French coincidence, from coincider, from Medieval Latin coincidere (see coincide). From 1640s as "occurrence or existence during the same time." Meaning "a concurrence of events with no apparent connection" is from 1680s, perhaps first in writings of Sir Thomas Browne.
coincident (adj.): late 16c., from French coincident, from coincider (see coincide).
coincidental (adj.): c. 1800, from coincident + -al (1).
coincidentally (adv.): 1837, from coincidental + -ly (2).
coincidently: 1620s, from coincident + -ly (2).
Cointreau (n.): orange-flavored liqueur, named for founders Adolphe and Edouard-Jean Cointreau, brothers from Angers, France, who set up Cointreau Distillery in 1849. The orange liqueur dates from 1875.
coir (n.): "prepared coconut fiber," 1580s, from Malayalam kayar "cord," from kayaru "to be twisted."
coit (n.): "coition," early 15c., from Latin coitus "going together," also "coition," from coire "to go together" (see coitus).