Etymology
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coitus (n.)

"copulation, sexual intercourse," 1848, scientific use of Latin coitus "a meeting together; sexual union," past participle of coire "to come together, meet," from assimilated form of com "together" (see co-) + ire (past participle itus) "to come, to go," (from PIE root *ei- "to go").

In Middle English nativized as coite (early 15c.). Coitus was used in English in general senses of "meeting, uniting," and also in reference to magnetic force, planetary conjunction, etc., before the sexual sense came to predominate.

Coitus interruptus, "sexual intercourse in which the penis is voluntarily withdrawn from the vagina before ejaculation, for the purpose of avoiding conception," is from 1886 (from 1885 in German publications). Coitus reservatus in reference to prolonged copulation by deliberate control is from 1890 in English (1880 in German).

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coit (n.1)

"coition," early 15c., from Latin coitus "going together," also "coition," from coire "to go together" (see coitus).

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coition (n.)

1540s, "a going together, a coming together," from Late Latin coitionem (nominative coitio) "a coming together, a meeting; copulation," noun of action from coitus, past participle of coire "to go together, come together" (see coitus). Sexual meaning "copulation" is attested in English from 1610s (coiture in the same sense is from 1570s).

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*ei- 
Proto-Indo-European root meaning "to go."

It forms all or part of: Abitur; adit; ambience; ambient; ambit; ambition; ambitious; andante; anion; cation; circuit; coitus; commence; commencement; concomitant; constable; count (n.1) title of nobility; county; dysprosium; errant; exit; initial; initiate; initiation; introit; ion; issue; itinerant; itinerary; janitor; January; Janus; Jena; Mahayana; obiter; obituary; perish; praetor; Praetorian; preterite; sedition; sudden; trance; transient; transit; transitive; viscount.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit e'ti "goes," imas "we go," ayanam "a going, way;" Avestan ae'iti "goes," Old Persian aitiy "goes;" Greek ienai "to go;" Latin ire "to go," iter "a way;" Old Irish ethaim "I go," Irish bothar "a road" (from *bou-itro- "cows' way"), Gaulish eimu "we go;" Lithuanian eiti "to go;" Old Church Slavonic iti "go;" Bulgarian ida "I go;" Russian idti "to go;" Gothic iddja "went."
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withdrawal (n.)
1820s, "act of taking back," also "retraction of a statement," from withdraw + -al (2). Earlier words in the same sense were withdrawment (1640s); withdraught (mid-14c.). Meaning "removal of money from a bank, etc." is from 1861; psychological sense is from 1916; meaning "physical reaction to the cessation of an addictive substance" is from 1929 (with an isolated use from 1897; withdrawal symptom is from 1910). As a synonym for coitus interruptus from 1889.
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berk (n.)

"fool," 1936, abbreviation of Berkshire Hunt (or Berkeley Hunt), rhyming slang for cunt but typically applied only to contemptible persons, not to the body part.

This is not an objective, anatomical term, neither does it imply coitus. It connects with that extension of meaning of the unprintable, a fool, or a person whom one does not like. ["Dictionary of Rhyming Slang," 1960]
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onanism (n.)

"masturbation," also "coitus interruptus," 1727, from Onan, name of the son of Judah (Genesis xxxviii.9), who spilled his seed on the ground rather than impregnate his dead brother's wife: "And Onan knew that the seed should not be his; and it came to pass, when he went in unto his brother's wife, that he spilled it on the ground, lest that he should give seed to his brother." The moral point of the verse was redirected by those who sought to suppress masturbation. Related: Onanist; onanistic.

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