Etymology
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contact (n.)

1620s, "action, state, or condition of touching," from Latin contactus "a touching" (especially "a touching of something unclean, contamination"), from past participle of contingere "to touch, seize," from assimilated form of com "with, together" (see con-) + tangere "to touch," from PIE root *tag- "to touch, handle."

The figurative sense of "a connection, communication" is attested from 1818. The meaning "a person who can be called upon for assistance" is attested by 1931. As a call to the person about to spin an aircraft propeller to signal that the ignition is switched on, contact was in use by 1913.

To make contact (1860) originally was in reference to electrical circuits. Contact lens " thin artificial lens placed directly on the surface of the eye to correct visual defects" is first recorded 1888, in a translation of an article published in Zurich in 1887 by A. Eugen Fick; contacts for "contact lenses" is from 1957. Contact sport, for one involving bodily contact, is attested from 1922.

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concision (n.)

late 14c., "a cutting away, mutilation," also, from 16c., "circumcision," from Late Latin concisionem (nominative concisio) "a separation into divisions, a mutilation," literally "a cutting up," noun of action from past participle stem of Latin concidere "to cut off, cut up, cut through, cut to pieces," from assimilated form of com-, here perhaps an intensive prefix (see con-), + caedere "to cut" (from PIE root *kae-id- "to strike"). From 18c. it began to be used in the sense of conciseness (q.v.).

Beware of dogs, beware of evil workers, beware of the concision. For we are the circumcision, which worship God in the spirit, and rejoice in Christ Jesus, and have no confidence in the flesh. [Philippians iii.2-3]

In Philippians iii.2 it translates Greek katatomē, a contemptuous substitution for the usual peritomē "circumcision," in reference to the Judaizing teachers who taught that Christian converts must first be circumcised.

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conductor (n.)

1520s, "one who leads or guides," from French conductour (14c., Old French conduitor), from Latin conductor "one who hires, contractor," in Late Latin "a carrier," from conductus, past participle of conducere "to lead or bring together, contribute, serve," from assimilated form of com "with, together" (see con-) + ducere "to lead" (from PIE root *deuk- "to lead").

Earlier in same sense was conduitour (early 15c., from Old French conduitor). Meaning "a director or manager" is from 1630s; specific sense of "leader of an orchestra or chorus" is from 1784. Meaning "one who has charge of passengers and collects fares on a railroad" is 1832, American English. Physics sense of "object or device that passes heat or other energy" is from 1745; of electricity from 1737.

The office of conductor in the modern sense was not clearly distinguished from that of leader until about 1800; formerly the leader played an instrument, usually the harpsichord [Century Dictionary]
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contagion (n.)

late 14c., "a communicable disease; a harmful or corrupting influence," from Old French contagion and directly from Latin contagionem (nominative contagio) "a touching, contact," often in a bad sense, "a contact with something physically or morally unclean, contagion," from contingere "to touch," from assimilated form of com "with, together" (see con-) + tangere "to touch," from PIE root *tag- "to touch, handle." Meaning "infectious contact or communication" is from 1620s.

A distinction between contagion and infection is sometimes adopted, the former being limited to the transmission of disease by actual contact of the diseased part with a healthy absorbent or abraded surface, and the latter to transmission through the atmosphere by floating germs or miasmata. There are, however, cases of transmission which do not fall under either of these divisions, and there are some which fall under both. In common use no precise discrimination of the two words is attempted. [Century Dictionary, 1897]
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conversion (n.)

mid-14c., originally of religion, "a radical and complete change in spirit, purpose, and direction of life away from sin and toward love of God," from Old French conversion "change, transformation, entry into religious life; way of life, behavior; dwelling, residence; sexual intercourse," from Latin conversionem (nominative conversio) "a turning round, revolving; alteration, change," noun of action from past-participle stem of convertere "to turn around; to transform," from assimilated form of com "with, together" (see con-) + vertere "to turn" (from PIE root *wer- (2) "to turn, bend").

Sense of "a change from one religion to another" (especially to Christianity) is from c. 1400 in English. General sense of "transformation, a turning or changing from one state to another" is from early 15c. In reference to the use of a building, from 1921. Conversion disorder "hysteria" (attested from 1946 but said to have been coined by Freud) was in DSM-IV (1994). Conversion therapy in reference to homosexuality is by 1979.

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concern (v.)

early 15c., of persons, "to perceive, distinguish;" also, of things, "to refer to, relate to, pertain to," from Old French concerner (15c.) and directly from Medieval Latin concernere "concern, touch, belong to," figurative use of Late Latin concernere "to sift, mix as in a sieve," from assimilated form of Latin com "with, together" (see con-) + cernere "to sift," hence "perceive, comprehend" (from PIE root *krei- "to sieve," thus "discriminate, distinguish").

Apparently the sense of the first element shifted to intensive in Medieval Latin. From late 15c. as "to affect the interest of, be of importance to;" hence the meaning "to worry, disturb, make uneasy or anxious" (17c.). Reflexive use "busy, occupy, engage" ("concern oneself") is from 1630s. Related: Concerned; concerning.

Used imperatively from 1803 (compare similar use of confound); often rendered in dialect as consarn (1832), probably a euphemism for damn (compare concerned). Letter opening to whom it may concern attested by 1740.

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conduct (v.)
Origin and meaning of conduct

early 15c., "to guide, accompany and show the way," from Latin conductus, past participle of conducere "to lead or bring together; contribute, serve," from assimilated form of com "with, together" (see con-) + ducere "to lead" (from PIE root *deuk- "to lead").

Sense of "to lead, command, direct, manage" is from mid-15c., originally military. General meaning "to direct, manage, act as leader of" is from 1630s; especially of a musical performance (1791).

Meaning "behave in a certain way" is from 1710. In physics, "to carry, convey, transmit," 1740. Related: Conducted; conducting. An earlier verb in the same sense was condyten (c. 1400), which goes with conduit.

To conduct is to lead along, hence to attend with personal supervision; it implies the determination of the main features of administration and the securing of thoroughness in those who carry out the commands; it is used of both large things and small, but generally refers to a definite task, coming to an end or issue: as, to conduct a religious service, a funeral, a campaign. [Century Dictionary]
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condescend (v.)

mid-14c., of God, a king., etc., "make gracious allowance" for human frailty, etc.; late 14c., "yield deferentially," from Old French condescendere (14c.) "to agree, consent, give in, yield, come down from one's rights or claims," and directly from Late Latin condescendere "to let oneself down, stoop," in Medieval Latin "be complaisant or compliant," from assimilated form of Latin com "with, together" (see con-) + descendere "to descend," literally "climb down," from de "down" (see de-) + scandere "to climb," from PIE root *skand- "jump" (see scan (v.)).

Sense of ""voluntarily waive ceremony or dignity proper to one's superior position or rank and willingly assume equality with inferiors" is from early 15c. Generally a positive word in Middle English; the modern, negative sense is from the notion of a mere show or assumed air of condescending (compare sense evolution in patronize). Also in Middle English "give one's consent; come to mutual agreement; make a concession."

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conversation (n.)

mid-14c., "place where one lives or dwells," also "general course of actions or habits, manner of conducting oneself in the world," both senses now obsolete; from Old French conversacion "behavior, life, way of life, monastic life," and directly from Latin conversationem (nominative conversatio) "frequent use, frequent abode in a place, intercourse, conversation," noun of action from past-participle stem of conversari "to live, dwell, live with, keep company with," passive voice of conversare "to turn about, turn about with," from assimilated form of com "with, together" (see con-) + versare, frequentative of vertere "to turn" (from PIE root *wer- (2) "to turn, bend").

Sense of "informal interchange of thoughts and sentiments by spoken words" is from 1570s. Used as a synonym for "sexual intercourse" from at least late 14c., hence criminal conversation, a legal term for adultery from late 18c. Conversation-piece is from 1712 as "painting representing a group of figures arranged as if in conversation;" 1784 as "subject for conversation, something to talk about."

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condition (n.)

mid-14c., condicioun, "particular mode of being of a person or thing," also "a requisite or prerequisite, a stipulation," from Old French condicion "stipulation; state; behavior; social status" (12c., Modern French condition), from Medieval Latin conditionem (nominative conditio), properly condicio "agreement; stipulation; the external position, situation, rank, place, circumstances" of persons, "situation, condition, nature, manner" of things, from condicere "to speak with, talk together, agree upon," in Late Latin "consent, assent," from assimilated form of com "together" (see con-) + dicere "to speak" (from PIE root *deik- "to show," also "pronounce solemnly").

Classical Latin condicio was confused in Late Latin with conditio "a making," from conditus, past participle of condere "to put together." The sense evolution in Latin apparently was from "stipulation" to "situation, mode of being."

Meaning "rank or state with respect to ordered society" is from late 14c. in English. From the notion of "prerequisite" comes the sense of "a restricting or limiting circumstance" (late 14c.). Also in Middle English "personal character, disposition" (mid-14c.).

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