An Etymological Dictionary of Astronomy and Astrophysics

1a) An assemblage or combination of things or parts forming a complex or unitary whole.

1b) An ordered and comprehensive assemblage of facts, principles, doctrines, or the like in a particular field of knowledge or thought (Dictionary.com).

2. Physics: An aggregate composed of physical bodies which we isolate, in our mind, from the region external to it in order to analyze physical situations. Everything outside the system which has a direct bearing on its behavior is called the → environment.
   

3. Astro.: An entity composed of a number of astronomical objects associated and acting together according to certain natural laws.
   

4. Computers: A system consisting of components (a combination of the hardware, software, and firmware) which are connected together in order to accomplish a specific function or set of functions.

Etymology (EN): From L.L. systema “an arrangement, a whole consisting of several parts,” from Gk. systema “arrangement, organized whole,” from sy-, variant of syn- “together” + ste- variant stem of histanai “to cause to stand” (from PIE base *sta- “to stand;” cf. Pers. ist, istâdan “to stand;” Mid.Pers. êstâtan;
O.Pers./Av. sta- “to stand, stand still; set;” Av. hištaiti; cf. Skt. sthâ- “to stand;” Gk. histemi “put, place, weigh,” stasis “a standing still;” L. stare “to stand;” Lith. statau “place;” Goth. standan; PIE base *sta- “to stand”) + -ma nominal suffix denoting result of action.

Etymology (PE): Râžmân, from raž, from Av. rāz- “to direct, put in line, set,” rasman- “the lines or files of the army,” razan “rule, order” (variants raj, râž, rak, râk, rezg (Lori), radé, râdé “line, rule, row,” rasté, râsté “row, a market with regular ranges of shops;” ris, risé “straight”), related to râst “right, true; just, upright, straight;” Mid.Pers. râst “true, straight, direct,” rây-, râyênitan “to arrange;” Sogdian rəšt “right;”
O.Pers. rāsta- “straight, true,” rās- “to be right, straight, true;” cf. Skt. raj- “to direct, stretch,” rjuyant- “walking straight;” Gk. orektos “stretched out;” L. regere “to lead straight, guide, rule,” p.p. rectus “right, straight;” PIE base *reg- “move in a straight line,” hence, “to direct, rule;” + -mân verbal noun suffix used with present and past stems, as in zâymân, câymân, sâxtemân, goftemân.