c. 1400, from Old French separacion (Modern French séparation), 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").
Specific sense of "sundering of a married couple" is attested from c. 1600. Sense in photography 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). Separation anxiety is attested from 1943.
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.
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."
1640s, "act of dividing," from divide (v.). Meaning "watershed, separation between river valleys" is recorded by 1807, American English.
late 14c., "separation, parting," from Old French desevrance, from dessevrer (see dissever).
"the severance of association or connection," 1610s, from French dissociation, from Latin dissociationem (nominative dissociatio) "a separation," noun of action from past-participle stem of dissociare (see dissociate).