mid-15c., “pertaining to the sun,” from Latin solaris “of the sun,” from sol “sun” (see sol). Meaning “living room on an upper story” is from Old English, from Latin solarium (see solarium). Old English had sunlic “solar.” Astrological sense from 1620s. Meaning “operated by means of the sun” is from 1740; solar power is attested from 1915, solar cell from 1955, solar panel from 1964. Solar system is attested from c.1704; solar wind is from 1958. Solar plexus (1771) “complex of nerves in the pit of the stomach,” apparently so called from its central position in the body (see plexus).
1680s, Modern Latin, literally “braid, network,” noun use of past participle of Latin plectere “to twine, braid, fold” (see complex (adj.)); used of a network, such as solar plexus “network of nerves in the abdomen” (see solar). Related: Plexal.
1610s “the whole creation, the universe,” from Late Latin systema “an arrangement, system,” from Greek systema “organized whole, a whole compounded of parts,” from stem of synistanai “to place together, organize, form in order,” from syn- “together” (see syn-) + root of histanai “cause to stand” from PIE root *sta- “to stand” (see stet). Meaning “set of correlated principles, facts, ideas, etc.” first recorded 1630s. Meaning “animal body as an organized whole, sum of the vital processes in an organism” is recorded from 1680s; hence figurative phrase to get (something) out of one’s system (1900). Computer sense of “group of related programs” is recorded from 1963. All systems go (1962) is from U.S. space program. The system “prevailing social order” is from 1806.