Etymology
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separation (n.)

c. 1400, separacioun, "a severing, detaching, cutting apart, act of removing or disconnecting one thing from another," from Old French separacion (Modern French séparation) and directly from Latin separationem (nominative separatio) noun of action from past-participle stem of separare "to pull apart," from se- "apart" (see secret (n.)) + parare "make ready, prepare" (from PIE root *pere- (1) "to produce, procure"). Alternative separateness (1650s) tends to hold to the meaning "distinct character or state, fact of being separate."

The specific sense of "sundering of a married couple, limited divorce" (without dissolution of the marriage tie) is attested from c. 1600. Sense in printing in reference to proportionate monochrome representations of a color photograph   is from 1922.

Separation of powers is attested by 1792, from French séparée de la puissance (Montesquieu, 1748). The idea was discussed in several places in "The Federalist" (1788), but not in that exact phrase (e.g. separation of the departments of power, No. 81). In psychology, the child's separation anxiety is attested from 1943.

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separationist (n.)

"one who advocates or favors separation" in any sense, 1831, from separation + -ist. Related: Separationism.

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divorce (n.)

late 14c., "legal dissolution of the bond of marriage," from Old French divorce (14c.), from Latin divortium "separation, dissolution of marriage," from divertere "to separate, leave one's husband, turn aside" (see divert). Not distinguished in English from legal separation until mid-19c. Extended sense of "complete separation, absolute disjunction" is from early 15c.

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parting (n.)

mid-13c., "the act of going away, departure;" c. 1300, "separation of persons, leave-taking," also "the act of dividing or putting asunder; distribution, apportionment;" verbal noun from part (v.). From late 14c. as "the act or process of dividing; a division or separation; a dividing line, a point or place of separation or division."

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disunity (n.)

"want of unity, state of separation; absence of accord," 1630s, from dis- + unity.

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divide (n.)

1640s, "act of dividing," from divide (v.). Meaning "watershed, separation between river valleys" is recorded by 1807, American English.

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aught (n.2)
"nothing, zero," faulty separation of a naught (see naught). See adder for similar misdivisions.
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disseverance (n.)

late 14c., "separation, parting," from Old French desevrance, from dessevrer (see dissever).

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segregation (n.)

1550s, "act of separating" (a sense now obsolete); 1610s, "act or action of segregating, separation from others," from Late Latin segregationem (nominative segregatio), noun of action from past-participle stem of segregare (see segregate). Meaning "state or condition of being segregated" is from 1660s. Specific U.S. sense of "enforced separation of races" is attested from 1883.

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separative 

"tending to separate," 1590s, from French séparatif (16c.), from Late Latin separativus "pertaining to separation," from Latin separare "to pull apart" (see separate (v.)).

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