Online Etymology Dictionary

conglomerate (n.): "large business group," 1967, from conglomerate (adj.).
conglomerate (v.): 1590s, from Latin conglomeratus, past participle of conglomerare (see conglomerate (adj.)). Related: Conglomerated; conglomerating.
conglomeration (n.): 1620s, from Latin conglomerationem (nominative conglomeratio), noun of action from past participle stem of conglomerare (see conglomerate (adj.)).
Congo: African nation, named for the river that runs through it, which is from a Bantu word meaning "mountains" (i.e., the river that flows from the mountains). As an adjective, Congoese is native English (1797) but has been supplanted by Congolese (1900), from French Congolais.
congrats (n.): 1884, colloquial shortening of congratulations. Further colloquialized in British English to congratters (1906) and among online gamers to grats (by 2000).
congratulate (v.): 1540s, from Latin congratulatus, past participle of congratulari "to congratulate" (see congratulation). Related: Congratulated; congratulating.
congratulation (n.): mid-15c., from Latin congratulationem (nominative congratulatio), noun of action from past participle stem of congratulari "wish joy," from com- "together, with" (see com-) + gratulari "give thanks, show joy," from gratus "agreeable" (see grace (n.)).
congratulations: 1630s, an exclamation conveying a sentiment of congratulation, from congratulation (q.v.).
congratulatory (adj.): 1520s; see congratulate + -ory.
congregate (v.): mid-15c., from Latin congregatus "flocking together," past participle of congregare "to herd together, collect in a flock, swarm; assemble," from com- "together" (see com-) + gregare "to collect into a flock, gather," from grex (genitive gregis) "a flock" (see gregarious). Related: Congregated; congregating.
congregation (n.): mid-14c., "a gathering, assembly," from Old French congregacion (12c., Modern French congrégation), from Latin congregationem (nominative congregatio), noun of action from congregare (see congregate).

Used by Tyndale to translate Greek ekklesia in New Testament and by some Old Testament translators in place of synagoge. (Vulgate uses a variety of words in these cases, including congregatio but also ecclesia, vulgus, synagoga, populus.) Protestant reformers in 16c. used it in place of church; hence the word's main modern sense of "local society of believers" (1520s).
congregational (adj.): 1630s, in reference to Congregationalism, a Protestant movement in which church congregations were to be self-governing (the term most used in New England, in Britain they were called Independent); from congregation + -al (1). Related: Congregationalist.
congress (n.): c. 1400, "body of attendants; also "meeting of armed forces" (mid-15c.); main modern sense of "coming together of people, a meeting" is from 1520s; from Latin congressus "a friendly meeting; a hostile encounter," past participle of congredi "meet with, fight with," from com- "together" (see com-) + gradi "to walk," from gradus "a step" (see grade (n.)).

Sense of "meeting of delegates" is first recorded 1670s. Meaning "sexual union" is from 1580s. Used in reference to the national legislative body of the American states since 1775 (though since 1765 in America as a name for proposed bodies). Congress of Vienna met Nov. 1, 1814, to June 8, 1815, and redrew the map of Europe with an eye to creating a balance of powers after the disruptions of Napoleon.
congressional (adj.): 1690s, from Latin congressionem (from congressus, see congress) + -al (1). Originally sometimes reviled as barbarous, Pickering (1816) quotes an unnamed English correspondent: "The term Congress belonging to America, the Americans may employ its derivatives, without waiting for the assent of the English."
congressman (n.): 1780, in reference to members of U.S. Congress, and it first appears in a piece of abuse (written by a Loyalist):
Ye coxcomb Congressmen, declaimers keen,
Brisk puppets of the Philadelphia scene ...
Congresswoman attested from 1918 (Jeannette Rankin (1880-1973) was the first).
Congreve: in reference to rockets or matches, from Sir William Congreve (1772-1828).
congruence (n.): mid-15c., from Latin congruentia "agreement, harmony, congruity," from congruentem (nominative congruens), present participle of congruere "to come together" (see congruent). Related: Congruency.
congruent (adj.): early 15c., "suitable, proper," from Latin congruentem (nominative congruens) "agreeing, fit, suitable," present participle of congruere, literally "to come together, agree, correspond with," from com- "with" (see com-) + a lost verb *gruere, *ruere "fall, rush," perhaps from PIE *ghrei- "to rub, grind" (see chrism). Geometry sense attested by 1706.
congruity (n.): late 14c., from Old French congruité "relevance, appropriateness," from Late Latin congruitatem (nominative congruens) "agreement," from congruus (see congruent).
congruous (adj.): c. 1600, from Latin stem congru- (see congruent) + -ous.
conic (adj.): 1560s, "pertaining to a cone," from Latin conicus, from Greek konikos "cone-shaped," from konos (see cone).
conical (adj.): 1560s, "pertaining to a cone," also "having the shape of a cone," from conic + -al (1).
conifer (n.): 1851, from Latin conifer "cone-bearing, bearing conical fruit," from conus "cone" (see cone) + ferre "to bear, carry" (see infer).
coniferous (adj.): 1660s, from conifer + -ous.
conject (v.): late 14c., obsolete verb replaced by conjecture (v.). Also in form congette.
conjectural (adj.): 1550s, from Latin conjecturalis "belonging to conjecture," from conjectura (see conjecture). Related: Conjecturally (mid-15c.).
conjecture (n.): late 14c., "interpretation of signs and omens," from Old French conjecture "surmise, guess," or directly from Latin coniectura "conclusion, interpretation, guess, inference," literally "a casting together (of facts, etc.)," from coniectus, past participle of conicere "to throw together," from com- "together" (see com-) + iacere "to throw" (see jet (v.)). Sense of "forming of opinion without proof" is 1530s.
conjecture (v.): early 15c., from conjecture (n.). In Middle English also with a parallel conjecte (n.), conjecten (v.). Related: Conjectured; conjecturing.
conjoin (v.): late 14c., from Old French conjoindre "meet, come together" (12c.), from Latin coniungere "to join together," from com- "together" (see com-) + iungere "join" (see jugular). Related: Conjoined, conjoining.
conjoint (adj.): late 14c., from Middle French conjoint, past participle of conjoindre (see conjoin). Related: Conjointly (early 14c.).
conjugal (adj.): 1540s, from Middle French conjugal (13c.), from Latin coniugalis "relating to marriage," from coniunx (genitive coniugis) "spouse," related to coniugare "to join together," from com- "together" (see com-) + iugare "to join," from iugum "yoke" (see jugular).
conjugate (v.): 1520s, in grammatical sense; 1560s in literal sense, from Latin coniugatus, past participle of coniugare "to yoke together" (see conjugal). Earlier as an adjective (late 15c.). Related: Conjugated; conjugating.
conjugation (n.): mid-15c., from Latin conjugationem (nominative conjugatio) "a combining, connecting," noun of action from conjugare "to join together" (see conjugal). Grammatical sense is 1520s.
conjunct (adj.): mid-15c., from Latin coniunctus, past participle of coniugare (see conjugal). A doublet of conjoint.
conjunction (n.): late 14c., originally of planets, from Old French conjonction "union, joining, sexual intercourse" (12c.), from Latin coniunctionem (nominative coniunctio), from past participle stem of coniugare "join together" (see conjugal). Compare Italian congiunzione, Spanish conjunción. Grammatical sense (late 14c.) was in Latin, a loan-translation of Greek syndesmos. The word also had the meaning "sexual union" 17c.-18c.
conjunctiva (n.): 1540s, medical Latin, short for membrana conjunctiva "conjunctive membrane" (see conjunctive).
conjunctive (adj.): late 15c., from Latin coniunctivus "serving to connect," from coniunctus, past participle of coniungere (see conjoin). Grammatical sense is from 1660s.
conjunctivitis (n.): 1835, inflammation of the conjunctiva; from conjunctiva + -itis "inflammation."
conjuncture (n.): c. 1600, from French conjoncture (16c.), from Modern Latin *conjunctura, from Latin coniunctus (see conjunct).
conjuration (n.): late 14c., coniuracioun, "conspiracy" (now obsolete), also "a calling upon something supernatural," from Old French conjuracion "spell, incantation, formula used in exorcism," from Latin coniurationem (nominative coniuratio) "a swearing together, conspiracy," noun of action from coniurare (see conjure).
conjure (v.): late 13c., "command on oath," from Old French conjurer "invoke, conjure" (12c.), from Latin coniurare "to swear together; conspire," from com- "together" (see com-) + iurare "to swear" (see jury (n.)). Magical sense is c. 1300, for "constraining by spell" a demon to do one's bidding. Related: Conjured; conjuring. Phrase conjure up "cause to appear in the mind" (as if by magic) attested from 1580s.
conjurer (n.): late 14c., from Anglo-French conjurour, Old French conjureur "conjurer, magician, exorcist," from Latin coniurator, from coniurare (see conjure).
conk (v.): as in conk out, 1918, coined by World War I airmen, perhaps in imitation of the sound of a stalling motor, reinforced by conk (v.) "hit on the head," originally "punch in the nose" (1821), from conk (n.), slang for "nose" (1812), perhaps from fancied resemblance to a conch (pronounced "conk") shell.
conker (n.): "snail shell," also "horse chestnut," from children's game of conkers (q.v.).
conkers (n.): "child's game played with horse chestnuts," originally with snail shells, 1847, probably a variant of conquer. The goal was to break the other player's item by hitting it with yours.
conlang (n.): by 1991, from constructed language.
connate (adj.): 1640s, from Late Latin connatus "born together, twins," past participle of connasci "to be born together," from com- "together" (see com-) + nasci "to be born" (Old Latin gnasci; see genus). Related: Connation.
connect (v.): mid-15c., from Latin conectere "join together" (see connection). Displaced 16c. by connex (1540s), from Middle French connexer, from Latin *connexare, a supposed frequentative of conectere (past participle stem connex-). Connect was re-established 1670s.

A similar change took place in French, where connexer was superseded by connecter. Meaning "to establish a relationship" (with) is from 1881. Slang meaning "get in touch with" is attested by 1926, from telephone connections. Meaning "awaken meaningful emotions, establish rapport" is from 1942. Of a hit or blow, "to reach the target," from c. 1920. Related: Connected; connecting; connectedness.
Connecticut: U.S. state, originally the name of the river, said to be from Mohican (Algonquian) quinnitukqut "at the long tidal river," from *kwen- "long" + *-ehtekw "tidal river" + *-enk "place."
connection (n.): Middle English conneccion (late 14c.), also connexioun (mid-15c.), from Old French connexion, from Latin connexionem (nominative connexio) "a binding or joining together," from *connexare, frequentative of conectere "to fasten together, to tie, join together," from com- "together" (see com-) + nectere "to bind, tie" (see nexus).

Spelling shifted from connexion to connection (especially in American English) mid-18c. under influence of connect, abetted by affection, direction, etc. See -xion.