An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) The Earth with its inhabitants. Compare → cosmos and → Universe.
2) Other planets, particularly → exoplanets.
3) Any realm, or domain, with all pertaining to it.
4) Physics: The → space-time in four dimensions, as distinguished from three-dimensional space. → world line.

M.E.; O.E. woruld, weorold; cf. O.S. werold, O.Fris. warld, Du. wereld, O.N. verold, O.H.G. weralt, Ger. Welt.

Jahân, variants keyhân, geyhân "world," giti "world, material world, time;" Mid.Pers. gêhân "world," gêtig "the material world; wordly," Manichean Mid.Pers. gyh "world," gyh'n "worlds;" Av. gaēθā- "being, world, matter, mankind" (O.Pers. gaiθā- "livestock"), gaya- "life, manner of living," root gay- "to live" (present tense jiva-), cognate with Skt. jīv- "to live," jīva- "alive, living;" Gk. bios "life," L. vivus "living, alive," vita "life;" PIE base *g^wei- "to live" (cf. O.E. cwic "alive;" O.C.S. zivo "to live;" Lith. gyvas "living, alive;" O.Ir. bethu "life," bith "age, life, world;" Welsh byd "world"). The Pers. words zistan "to live," zendé "alive," zendegi "life," and jân "vital spirit, soul; mind" belong to this family.

In relativity, the path traced out in four-dimensional → space-time that represents a continuous sequence of events relating to a given particle. A point on a world line is called an → event. Any straight world line corresponds to an → inertial motion. Curved world lines represent → accelerated motion. A world line that curves corresponds to an accelerated observer. World lines are shown on space-time diagrams.

→ world; → line.