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.
updated on February 23, 2021