also caesium, rare alkaline metal, 1861, coined by Bunsen and Kirchhoff in 1860 in Modern Latin (caesium), from Latin caesius "blue-gray" (especially of eyes), in reference to the two prominent blue lines in its spectrum, by which it was first identified. With metallic element ending -ium. The first metal discovered by the aid of a spectroscope.
The dye is obtained from certain lichens. It is naturally blue but turns red in acid and is restored to blue by alkalis. Figurative use of litmus test is first attested 1957, from scientific use of litmus-treated paper as a chemical indicator. Litmus paper with this meaning is from 1803.
genus of plants native to Mexico and Central America, 1804, named 1791 by Spanish botanist Antonio José Cavanilles for Anders Dahl (1751-1789), Swedish botanist and pupil of Linnaeus, who discovered it for science in Mexico in 1788.
The likelihood that a true blue variety of the flower never could be cultivated was first proposed by French-Swiss botanist Augustin Pyramus de Candolle, and noted in English by 1835; hence blue dahlia, figurative expression for "something impossible or unattainable" (1843).
precious stone, a blue-to-transparent variety of corundum next in hardness to diamond, mid-13c., saphyr, from Old French saphir (12c.) and directly from Latin sapphirus (source also of Spanish zafir, Italian zaffiro), from Greek sappheiros, name of a blue precious stone, from a Semitic source (compare Hebrew sappir "sapphire"), but according to OED probably not ultimately from Semitic.
Some linguists propose an origin in Sanskrit sanipriya, a dark precious stone (perhaps sapphire or emerald), literally "sacred to Saturn," from Sani "Saturn" + priyah "precious." The gem meant by the Greeks apparently was not the one now so called, but perhaps rather lapis lazuli, the modern sapphire perhaps being signified by Greek hyakinthos. In Renaissance lapidaries, it was said to cure anger and stupidity. As an adjective from early 15c. As a color, a deep brilliant or bright blue, by 1680s. Related: Sapphiric.
"A coarse cotton stuff, generally blue, worn by sailors" [Century Dictionary, 1897], 1610s, dongerijns, from Hindi dungri "coarse calico," said to be from the name of a village, now one of the quarters of Bombay. Dungarees "trousers made of dungaree" is by 1868.
type of plant (in modern use Rubia tinctorum) yielding a valuable dyestuff, Old English mædere and Old Norse maðra, from PIE *modhro- "dye plant" (source also of Old High German matara "madder," Polish modry, Czech modry "blue").