rectangle (n.)

"space or difference in direction between intersecting lines," late 14c., from Old French angle "an angle, a corner" (12c.) and directly from Latin angulus "an angle, a corner," a diminutive form from PIE root *ang-/*ank- "to bend" (source also of Greek ankylos "bent, crooked," Latin ang(u)ere "to compress in a bend, fold, strangle;" Old Church Slavonic aglu "corner;" Lithuanian anka "loop;" Sanskrit ankah "hook, bent," angam "limb;" Old English ancleo "ankle;" Old High German ango "hook").

The figurative sense "point or direction from which one approaches something" is from 1872. Angle-bracket is attested by 1781 in carpentry; 1956 in typography.

mid-13c., "mason's tool for measuring right angles, carpenter's square," from Old French esquire "a square, squareness," from Vulgar Latin *exquadra, a back-formation from *exquadrare "to square," from Latin ex "out" (see ex-) + quadrare "make square, set in order, complete," from quadrus "a square" (from PIE root *kwetwer- "four").

The meaning "square shape or area" is recorded by late 14c. (Old English used feower-scyte). The geometric sense of "four-sided rectilinear figure" is from 1550s. The mathematical sense of "number or quantity derived from a number multiplied by itself" is also from 1550s.

As "square piece; any object in roughly square form" by c. 1600. As a body of troops, 1590s. As "old-fashioned person" by 1944 (see square adj.). As short for square meal, from 1882. Square one "the very beginning" (often what one must go back to) is from 1960, probably a figure from board games.

The sense of "quadrilateral open space in a town or park" is from 1680s; that of "area bounded by four streets in a city" is from c. 1700; in England this was often an individual building but in the U.S. commonly "a block of buildings bounded by four streets" (by 1867), which made it formerly noted as one of the words used differently in the two countries.