1891, "part of a house exposed to the sun," earlier "sundial" (1842), from L. solarium "sundial," also "a flat housetop," lit. "that which is exposed to the sun," from sol "sun" (see sol).
Main Entry: so·lar·i·um Pronunciation: sO-'lar-E-&m, s&-, -'ler- Function: noun Inflected Form: pluralso·lar·ia/-E-&/also-ums : a room (as in a hospital) used especially for sunbathing or therapeutic exposure to light