orb (n.)

mid-15c., "sphere, globe, something spherical or circular, orbit of a heavenly body," from Old French orbe "orb, globe" (13c.) and directly from Latin orbem (nominative orbis) "circle, disk, ring, hoop, orbit," probably related to orbita "wheel track, rut," a word of unknown and much-disputed origin. Watkins suggests a connection with the root of orchid. De Vaan suggests *horbi- "turning thing."

A three-dimensional extension of a word originally describing two-dimensional shapes. The ancient astronomical sense is in reference to the hollow "spheres" that carried each of the planets and the stars through their heavenly motions in the Ptolemaic system. Used poetically of the earth, sun, or moon from 1590s; used rhetorically of the eye from 1650s. As a verb from c. 1600.

Orb-weaver in reference to spiders that make webs formed of lines radiating from a central point (as distinguished from tube- or tunnel-weavers) is recorded from 1889.