Etymology
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encompass (v.)

"form a circle about, encircle," 1550s, from en- (1) "make, put in" + compass (n.). Related: Encompassed; encompasses; encompassing.

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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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circuity (n.)

"a movement in a circle," 1620s, from French circuite, from Medieval Latin circuitus (see circuitous) on model of gratuite, etc.

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rat-pack (n.)

1951, "a gang of disorderly young people" [OED], from rat (n.) + pack (n.). In reference to the Hollywood circle around Frank Sinatra, from 1958.

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semicircular (adj.)

also semi-circular, "having the form of a half-circle," early 15c., semicirculer, from Medieval Latin semicirculus (see semicircle) + -ar. Related: Semicircularly.

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gyre (n.)
1560s, "a circular motion," from Latin gyrus "circle, circular course, round, ring," from Greek gyros "a circle, ring," related to gyrós "rounded," perhaps from PIE root *geu- "to bend, curve" (source also of Armenian kor "crooked," Lithuanian gurnas "hip, ankle, bone," Norwegian kaure "a curly lock of hair"). The noun is attested in Middle English only in reference to ship's tackle (early 15c.).
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quadrant (n.)

late 14c., "a quarter of a day, six hours," from Old French quadrant, cadran, name of a Roman coin, also "a sundial," from Latin quadrantem (nominative quadrans) "a fourth part, a quarter," also the name of a coin worth a quarter of an as; noun use of the present participle of quadrare "to make square; put in order, arrange, complete; run parallel, be exact," figuratively "to fit, suit, be proper," related to quadrus "a square," quattuor "four" (from PIE root *kwetwer- "four").

From 1570s as "the quarter of a circle, the arc of a circle containing 90 degrees." The ancient surveying instrument for measuring altitudes is so called from c. 1400, because it forms a quarter circle. Related: Quadrantal.

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corral (v.)

1847, "to drive into a corral," from corral (n.). From 1848 as "to form a circle with wagons." Meaning "to lay hold of, collar, capture, make a prisoner of" is U.S. slang from 1860. Related: Corralled.

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encyclopedia (n.)

1530s, "general course of instruction," from Modern Latin encyclopaedia (c. 1500), thought to be a false reading by Latin authors of Greek enkyklios paideia taken as "general education," but literally "training in a circle," i.e. the "circle" of arts and sciences, the essentials of a liberal education; from enkyklios "circular," also "general" (from en "in;" see in + kyklos "circle;" from PIE root *kwel- (1) "revolve, move round") + paideia "education, child-rearing," from pais (genitive paidos) "child" (see pedo-).

Modern sense of "reference work arranged alphabetically" is from 1640s, often applied specifically to the French Encyclopédie ou Dictionnaire raisonné des Sciences, des Arts, et des Métiers (1751-65). Related: Encyclopedist.

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concentric (adj.)

"having a common center," c. 1400, from Old French concentrique, from Medieval Latin concentricus, from assimilated form of com "with, together" (see con-) + Latin centrum "circle, center" (see center (n.)).

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