Etymology
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sector (n.)

1560s, in geometry, "a section of a circle between two radii," from Late Latin sector "section of a circle," in classical Latin "a cutter, one who cuts," from sectus, past participle of secare "to cut" (from PIE root *sek- "to cut"). Sector translated Greek tomeus in Latin editions of Archimedes.

By 1715 of any figure having the shape of a sector; the meaning "area, division" (without regard to shape) is by 1920, perhaps generalized from a World War I military sense (1916) of "part of a front," based on a circle centered on a headquarters. The meaning "a branch of an economy" is by 1937. As a verb from 1884, "divide into sectors." Related: Sectored; sectoral; sectorial.

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*sek- 

Proto-Indo-European root meaning "to cut." It forms all or part of: bisect; dissect; hacksaw; insect; intersect; resect; saw (n.1) "cutting tool;" Saxon; scythe; secant; secateurs; sect; section; sector; sedge; segment; skin; skinflint; skinny; transect.

It is the hypothetical source of/evidence for its existence is provided by: Hittite shakk- "to know, pay attention to;" Latin secare "to cut," sectio "a cutting, cutting off, division;" Old Church Slavonic seko, sešti "to cut," sečivo "ax, hatchet," Russian seč' "to cut to pieces;" Lithuanian įsėkti "to engrave, carve;" Albanian šate "mattock;" Old Saxon segasna, Old English sigðe "scythe;" Old English secg "sword," seax "knife, short sword;" Old Irish doescim "I cut."

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Potsdam 

town in Germany, first recorded 993 as Poztupimi; the name is Slavic, the first element is po "by near," the second element evidently was influenced by Dutch names in -dam. The Potsdam Conference of the victorious Allies in World War II was held July 17-Aug. 2, 1945, to decide the fate of Germany. During the Cold War, the town was in the Soviet sector and the bridge there across the Havel was one of the restricted border crossings between East Germany and West Berlin. The Americans and the Soviets used it for the exchange of captured spies. 

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public (adj.)

late 14c., publike, "open to general observation," from Old French public (c. 1300) and directly from Latin publicus "of the people; of the state; done for the state," also "common, general, of or belonging to the people at large; ordinary, vulgar," and as a noun, "a commonwealth; public property." This Latin word was altered (probably by influence of Latin pubes "adult population, adult;" see pubis) from Old Latin poplicus "pertaining to the people," from populus "people" (see people (n.)).

Attested in English from early 15c. as "of or pertaining to the people at large" and from late 15c. as "pertaining to public affairs." The meaning "open to all in the community, to be shared or participated in by people at large" is from 1540s in English. An Old English adjective in this sense was folclic. The sense of "done or made by or on behalf of the community as a whole" is by 1550s; that of "regarding or directed to the interests of the community at large, patriotic" is from c. 1600.

Public relations "the management of the relationship between a company or corporation and the general public" is recorded by 1913 (with an isolated use by Thomas Jefferson in 1807). Public office "position held by a public official" is from 1821; public service is from 1570s; public interest "the common well-being" is from 1670s. Public enemy, one considered a nuisance to the general community, is attested from 1756. Public sector attested from 1949. Public funds (1713) are the funded debts of a government.

Public woman "prostitute" is by 1580s, on the notion of "open for the use of all." For public house, see pub.

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private (adj.)

late 14c., "pertaining or belonging to oneself, not shared, peculiar to an individual only;" of a thing, "not open to the public, for the use of privileged persons;" of a religious rule, "not shared by Christians generally, distinctive;" from Latin privatus "set apart (from what is public), belonging to oneself (not to the state), peculiar, personal," used in contrast to publicus, communis.

This is a past-participle adjective from the verb privare "to bereave, deprive, rob, strip" of anything; "to free, release, deliver" from anything, from privus "one's own, individual," from Proto-Italic *prei-wo- "separate, individual," from PIE *prai-, *prei- "in front of, before," from root *per- (1) "forward." The semantic shift would be from "being in front" to "being separate."

Old English in this sense had syndrig. Of persons, "not holding public office or employment," recorded from early 15c. Of communications, "meant to be secret or confidential," 1550s. In private "privily" is from 1580s. Related: Privately.

Private school "school owned and run by individuals, not by the government, and run for profit" is by 1650s. Private parts "the pudenda" is from 1785 (privete "the sexual parts" is from late 14c.; secret parts in the same sense is from 16c.).

Private property "property of persons in their individual, personal, or private capacity," as distinguished from property of the state or public or for public use, is by 1680s. Private enterprise "business or commercial activity privately owned and free from direct state control" is recorded by 1797; private sector "part of an economy, industry, etc. that is free from state control" is from 1948.

Private eye "private detective, person engaged unofficially in obtaining secret information for or guarding the private interests of those who employ him" is recorded from 1938, American English (Chandler). Private detective "detective who is not a member of an official police force" is by 1856.

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