/merr"kyeuh ree/ , n. , pl. mercuries .
1. Chem. a heavy, silver-white, highly toxic metallic element, the only one that is liquid at room temperature; quicksilver: used in barometers, thermometers, pesticides, pharmaceutical preparations, reflecting surfaces of mirrors, and dental fillings, in certain switches, lamps, and other electric apparatus, and as a laboratory catalyst. Symbol: Hg; at. wt.: 200.59; at. no.: 80; sp. gr.: 13.546 at 20°C; freezing point: -38.9°C; boiling point: 357°C.
2. Pharm. this metal as used in medicine, in the form of various organic and inorganic compounds, usually for skin infections.
3. ( cap. ) the ancient Roman god who served as messenger of the gods and was also the god of commerce, thievery, eloquence, and science, identified with the Greek god Hermes.
4. ( cap. ) Astron. the planet nearest the sun, having a diameter of 3031 mi. (4878 km), a mean distance from the sun of 36 million mi. (57.9 million km), and a period of revolution of 87.96 days, and having no satellites: the smallest planet in the solar system. See table under planet .
5. a messenger, esp. a carrier of news.
6. any plant belonging to the genus Mercurialis, of the spurge family, esp. the poisonous, weedy M. perennis of Europe.
7. Good-King-Henry.
8. ( cap. ) Aerospace. one of a series of U.S. spacecraft, carrying one astronaut, that achieved the first U.S. suborbital and orbital manned spaceflights.
[ 1300-50; ME Mercurie Mercurius, akin to merx goods ]