Etymology
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quad 

1820 as a shortening of quadrangle (n.) in the building-court sense (in this case "quadrangle of a college," Oxford student slang); also in old slang the quadrangle of a jail or prison, where prisoners take their exercise. By 1880 as short for the printer's quadrat (n.). By 1896 as "a quadricycle, a bicycle for four riders" (quadricycle is attested by 1879, quadruplet in this sense by 1893). As "one of four young at a single birth" by 1951 (in reference to armadillos), short for quadruplet; 1970 as a shortening of quadraphonic (adj.). Related: Quads.

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quod (n.)

"prison," c. 1700, a cant slang word of unknown origin; perhaps a variant of quad in the "building quadrangle" sense.

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quadri- 

before vowels quad- (before -p- often quadru-, from an older form in Latin), word-forming element used in compounds of Latin origin and meaning "four, four times, having four, consisting of four," from Latin quadri-, which is related to quattor "four" (from PIE root *kwetwer- "four").

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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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quadriplegic (adj.)

also quadraplegic, "person paralyzed in both arms and legs," 1897, from quadriplegia + -ic. A correct, all-Greek formation would be *tessaraplegic. The noun is first attested 1912, from the adjective.

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quadrat (n.)

"a blank, low-cast type used by typographers to fill in larger spaces at the end of or between printed lines," 1680s, from French quadrat "a quadrat," literally "a square," from Latin quadratrus, past participle of quadrare "to make square," related to quadrus "a square," quattuor "four" (from PIE root *kwetwer- "four"). Earlier in English it meant a type of surveying instrument with a square plate (c. 1400).

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quadratus (n.)

"a square-shaped muscle," 1727, from Latin quadratus "square, squared," past participle of quadrare "to square, make square; put in order," related to quadrus "a square," quattuor "four" (from PIE root *kwetwer- "four"). Especially the Quadratus femoris, the muscle situated at the back of the hip-joint.

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quadripartite (adj.)

early 15c., "divided into four parts," also "written in four identical versions" (of contracts, indentures, etc.), from Latin quadripartitus "divided into four parts, fourfold," from quadri- "four" (from PIE root *kwetwer- "four") + partitus, past participle of partiri "to divide" (from pars "a part, piece, a share," from PIE root *pere- (2) "to grant, allot"). Related: Quadripartition.

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quadricorn (adj.)

"having four horns," 1875; also, as a noun, "a four-horned animal or insect" (1848); see quadri- "four" + Latin cornus "horn" (from PIE root *ker- (1) "horn; head"). Alternative quadrucorn is older (c. 1600).

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quadrangular (adj.)

"four-cornered, four-sided," early 15c., quadrangulere, from Medieval Latin quadrangularis "having four corners," from Late Latin quadrangulus "having four angles" (see quadrangle). Related: Quadrangularly.

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