Origin and history of solarium

mid-15c., "of, pertaining to, or determined by the sun," from Latin solaris "of the sun," from sol "sun" (from PIE root *sawel- "the sun"). Meaning "living room on an upper story" (also sollar) is from Old English, from Latin solarium (see solarium). For "of or proceeding from the sun," the earlier word was Old English sunlic, Middle English sonneli. Solific (1550s) also has been used.

The meaning "operated by means of the sun or its heat" is from 1740; solar power is attested from 1915, solar cell as a photovoltaic device from 1955, solar panel, designed to absorb the sun's rays, is from 1964. The astronomical solar system "sun and the bodies revolving round or dependent on it" is attested from c. 1704; solar wind is so called 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).

word-forming element in chemistry, used to coin element names, from Latin adjectival suffix -ium (neuter of -ius), which formed metal names in Latin (ferrum "iron," aurum "gold," etc.). In late 18c chemists began to pay attention to the naming of their substances with words that indicate their chemical properties. Berzelius in 1811 proposed forming all element names in Modern Latin. As the names of some recently discovered metallic elements already were in Latin form (uranium, chromium, borium, etc.), the pattern of naming metallic elements in -ium or -um was maintained (in cadmium, lithium, plutonium, etc.; helium is an anomaly).