英语词源字典 - 在线词源网站

flatland (n.)[flatland 词源字典]: 1735, from flat (adj.) + land (n.). Edwin Abbott's popular book about an imaginary two-dimensional world was published in 1884.[flatland etymology, flatland origin, 英语词源]
orb (n.): mid-15c., "sphere, globe, something spherical or circular," 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," of unknown origin. Watkins suggests a connection with the root of orchid.

A three-dimensional extension of a word originally describing two-dimensional shapes. Astronomical sense is in reference to the hollow spheres that carried the planets and stars in the Ptolemaic system. As a verb from c. 1600. Orb weaver spider is first recorded 1889.
two (adj.): Old English twa "two," fem. and neuter form of twegen "two" (see twain), from Proto-Germanic *twa (cognates: Old Saxon and Old Frisian twene, twa, Old Norse tveir, tvau, Dutch twee, Old High German zwene, zwo, German zwei, Gothic twai), from PIE *duwo, variant of dwo "two" (cognates: Sanskrit dvau, Avestan dva, Greek duo, Latin duo, Old Welsh dou, Lithuanian dvi, Old Church Slavonic duva "two," first element in Hittite ta-ugash "two years old").

Two-fisted is from 1774. Two cheers for _____, expressing qualified enthusiasm first recorded 1951 in E.M. Forster's title "Two Cheers for Democracy." Two-dimensional is recorded from 1883; figurative sense of "lacking substance or depth" is attested from 1934.