Etymology
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intercourse (n.)

mid-15c., "communication to and fro," ("In early use exclusively with reference to trade" [OED]), from Old French entrecors "exchange, commerce, communication" (12c., Modern French entrecours), from Late Latin intercursus "a running between, intervention," in Medieval Latin "intercommunication," from intercursus, past participle of intercurrere "to run between, intervene, mediate," from Latin inter "between" (see inter-) + currere "to run" (from PIE root *kers- "to run").

Sense of "frequent and habitual meeting and contact, social communication between persons" is from 1540s. Meaning "mental or spiritual exchange or intercommunication" is from 1560s. Meaning "sexual relations" (1798) probably is a shortening of euphemistic sexual intercourse (1771) with intercourse in its sense "social contact and relations."

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non-intercourse (n.)

"a refraining from intercourse," in any sense, 1809, from non- + intercourse.

Non-Intercourse Act, an act of the United States Congress of 1809 passed in retaliation for claims made by France and Great Britain affecting the commerce of the United States, and particularly the personal rights of United States seamen, continued 1809 and 1810, and against Great Britain 1811. It prohibited the entry of merchant vessels belonging to those countries into the ports of the United States, and the importation of goods grown or manufactured in those countries. [Century Dictionary]
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sexual (adj.)

1650s, "distinctive of either sex, of or pertaining to the fact of being male or female," from Late Latin sexualis "relating to sex," from Latin sexus "a sex, state of being either male or female, gender" (see sex (n.)).

The meaning "pertaining to copulation or generation" is from 1766, on the notion of "done by means of the two sexes;" hence also "pertaining to erotic appetites and their gratification" and "peculiar to or affecting the organs of sex, venereal" (1799). The phrase sexual intercourse is attested by 1771 (see intercourse), sexual orientation by 1967, sexual harassment by 1975. Sexual revolution is attested by 1962. Sexual politics is from 1970. Related: Sexually.

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*kers- 

Proto-Indo-European root meaning "to run."

It forms all or part of: car; career; cargo; caricature; cark; carpenter; carriage; carrier; carry; charabanc; charette; charge; chariot; concourse; concur; concurrent; corral; corridor; corsair; courant; courier; course; currency; current; curriculum; cursive; cursor; cursory; discharge; discourse; encharge; excursion; hussar; incur; intercourse; kraal; miscarry; occur; precursor; recourse; recur; succor.

It is the hypothetical source of/evidence for its existence is provided by: Greek -khouros "running;" Latin currere "to run, move quickly;" Lithuanian karšiu, karšti "go quickly;"Old Irish and Middle Welsh carr "cart, wagon," Breton karr "chariot," Welsh carrog "torrent;" Old Norse horskr "swift."

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intercommunion (n.)

1749, "intimate intercourse, fellowship," from inter- "between" + communion (n.).

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converse (n.2)

c. 1500, "acquaintance by frequent or customary intercourse," from converse (v.). From 1610s as "conversation, familiar discourse."

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intimacy (n.)

1640s, from intimate (adj.) + abstract noun suffix -cy. Sense of "sexual intercourse" attested from 1670s but modern use is from newspaper euphemistic use (1882).

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cohabitation (n.)

mid-15c., cohabitacioun, "action or state of living together," from Old French cohabitacion "cohabitation; sexual intercourse," or directly 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" (from PIE root *ghabh- "to give or receive"). Specifically "state of living together as husband and wife without benefit of marriage," implying sexual intercourse, from 1540s.

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diplomatist (n.)

"person officially employed in international intercourse; one versed in the art of diplomacy," 1801, from French diplomatiste, from Latin diplomat-, stem of diploma (see diplomacy).

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