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.

1969, irregular hybrid formation from Latin-derived quadri- "four" + phonic, from Greek phonē "sound, voice" (from PIE root *bha- (2) "to speak, tell, say"). The goal was to reproduce front-to-back sound distribution in addition to side-to-side stereo. The later term for the same idea, surround sound, is preferable to this. Quadrasonic (1970) was at least not a hybrid. Related: Quadraphonics; quadraphony.

"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).

1650s, "square," with -ic + obsolete quadrate "a square; a group of four things" (late 14c.), from Latin quadratum, noun use of neuter adjective 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"). In mathematics by 1660s; the algebraic quadratic equations (1680s) are so called because they involve the square and no higher power of x.

"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.

1650s, "lasting four years, comprising four years;" as "happening once in four years," 1701; from quadri- + ending from biennial, etc. Correct formation would be quadriennial (compare Latin quadriennium "period of four years," which also is sometimes used in English). As a noun from 1640s. Quadrennium as "a period of four years" is by 1735. Related: Quadrennially.

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").

"pertaining to or consisting of a period of 400 years," as a noun, "commemoration or celebration of an event which occurred 400 years ago," also quadri-centennial, 1859, from quadri- + centennial. Alternative quater-centennial (1868, meaning "four times a year") is from Latin quater "four times" (compare quaternary).

1840, see quadricep.

large extensor muscle of the thigh, 1840, Modern Latin, from quadri- on model of bicep (q.v.). Related: Quadriceps. So called because divided into four parts.