Mercury

n. [Lat. Mercurius, said to be formed from merces, wares, or mercari, to traffic.]

1. (Rom. Myth.) The son of Jupiter and Maia, the messenger and interpreter of the gods, and the god of eloquence and of commerce; —called by the Greeks Hermes.
2. (Chem.) A certain metal, white like silver, liquid at common temperatures, and congealing at forty degrees below zero, on Fahrenheit's scale, and having a specific gravity of 13.6; quicksilver; hydrargyrum. It acts as a poison, and its compounds are largely used in medicine. It is found in nature usually in combination with sulphur, forming cinnabar; named by the alchemists after the god Mercury.
3. (Med.) A salt or preparation of mercury, used as a remedial agent, as calomel, blue-pill, &c.
4. (Astron.) One of the planets of the solar system, being the one nearest the sun, from which its mean distance is about 37,000,000 miles. Its period is 88 days, and its diameter 3000 miles.
5. A carrier of tidings; a news-boy; a messenger; hence, also, a newspaper.

At the reading-room of the British Museum he observes that among the books carried by the Mercury of the place to the students there. J. Stephens. 6. Sprightly or mercurial quality; warmth of temperament; spirit; uneasiness or mutability; fickleness. [Obs.] He was so full of mercury that he could not fix long in any friendship, or to any design. Barrett. 7. (Bot.) A plant (the Mercurialis annua), the leaves of which are sometimes used for spinach, in Europe. The name is also applied, in the United States, to certain climbing plants, some of which are poisonous to the skin, especially to the Rhus toxicodendron, or poison ivy. Horn mercury, a mineral chloride of mercury, having a semi-translucent, horn-like appearance.