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[mur-kyuh-ree] /ˈmɜr kyə ri/
noun, plural mercuries.
Chemistry. 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; atomic weight: 200.59; atomic number: 80; specific gravity: 13.546 at 20°C; freezing point: −38.9°C; boiling point: 357°C.
Pharmacology. this metal as used in medicine, in the form of various organic and inorganic compounds, usually for skin infections.
(initial capital letter) 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.
(initial capital letter) Astronomy. the planet nearest the sun, having a diameter of 3031 miles (4878 km), a mean distance from the sun of 36 million miles (57.9 million km), and a period of revolution of 87.96 days, and having no satellites: the smallest planet in the solar system.
a messenger, especially a carrier of news.
any plant belonging to the genus Mercurialis, of the spurge family, especially the poisonous, weedy M. perennis of Europe.
(initial capital letter) Aerospace. one of a series of U.S. spacecraft, carrying one astronaut, that achieved the first U.S. suborbital and orbital manned spaceflights.
Origin of mercury
1300-50; Middle English Mercurie < Medieval Latin, Latin Mercurius, akin to merx goods Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for mercury


noun (pl) -ries
Also called quicksilver, hydrargyrum. a heavy silvery-white toxic liquid metallic element occurring principally in cinnabar: used in thermometers, barometers, mercury-vapour lamps, and dental amalgams. Symbol: Hg; atomic no: 80; atomic wt: 200.59; valency: 1 or 2; relative density: 13.546; melting pt: –38.842°C; boiling pt: 357°C
any plant of the euphorbiaceous genus Mercurialis See dog's mercury
(archaic) a messenger or courier
Word Origin
C14: from Latin Mercurius messenger of Jupiter, god of commerce; related to merx merchandise


(Roman myth) the messenger of the gods Greek counterpart Hermes


the second smallest planet and the nearest to the sun. Mean distance from sun: 57.9 million km; period of revolution around sun: 88 days; period of axial rotation: 59 days; diameter and mass: 38 and 5.4 per cent that of earth respectively
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Word Origin and History for mercury


"the Roman god Mercury," mid-12c., from Latin Mercurius "Mercury," originally a god of tradesmen and thieves, from merx "merchandise" (see market (n.)); or perhaps [Klein, Tucker] from Etruscan and influenced by merx. Later he was associated with Greek Hermes. The planet closest to the sun so called in classical Latin (late 14c. in English). A hypothetical inhabitant of the planet was a Mercurean (1855) or a Mercurian (1868). For the metallic element, see mercury.


silver-white fluid metallic element, late 14c., from Medieval Latin mercurius, from Latin Mercurius (see Mercury). Prepared from cinnabar, it was one of the seven metals (bodies terrestrial) known to the ancients, which were coupled in astrology and alchemy with the seven known heavenly bodies. This one probably so associated for its mobility. The others were Sun/gold, Moon/silver, Mars/iron, Saturn/lead, Jupiter/tin, Venus/copper. The Greek name for it was hydrargyros "liquid silver," which gives the element its symbol, Hg. Cf. quicksilver.

Online Etymology Dictionary, © 2010 Douglas Harper
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mercury in Medicine

mercury mer·cu·ry (mûr'kyə-rē)
Symbol Hg
A silvery-white poisonous metallic element, liquid at room temperature and used in thermometers. Atomic number 80; atomic weight 200.59; melting point -38.83°C; boiling point 356.73°C; specific gravity 13.546 (at 20°C); valence 1, 2. Also called hydrargyrum.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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mercury in Science
Symbol Hg
A silvery-white, dense, poisonous metallic element that is a liquid at room temperature and is used in thermometers, barometers, batteries, and pesticides. Atomic number 80; atomic weight 200.59; melting point -38.87°C; boiling point 356.58°C; specific gravity 13.546 (at 20°C); valence 1, 2. See Periodic Table.

Our Living Language  : Like a few other elements, mercury has a chemical symbol, Hg, that bears no resemblance to its name. This is because Hg is an abbreviation of the Latin name of the element, which was hydrargium. This word in turn was taken over from Greek, where it literally meant "water-silver." With this name the Greeks were referring to the fact that mercury is a silvery liquid at room temperature, rather than a solid like other metals. Similarly, an older English name for this element is quicksilver, which means "living silver," referring to its ability to move like a living thing. (The word quick used to mean "alive," as in the Biblical phrase "the quick and the dead.") The name mercury refers to the fact that the element flows about quickly: the name comes from the Roman god Mercury, who was the swift-footed messenger of the gods.
The planet closest to the Sun and the second smallest in the solar system. Mercury is a terrestrial or inner planet, second in density only to Earth, with a rugged, heavily-cratered surface similar in appearance to Earth's Moon. Its rotational period of 58.6 days is two-thirds of its 88-day orbital period, thus, it makes three full axial rotations every two years. Mercury's atmosphere is almost nonexistent; this fact, which produces rapid radiational cooling on its dark side, together with its proximity to the Sun, gives it a temperature range greater than any other planet in the solar system, from 466° to -184°C (870° to -300°F). Because it is so close to the Sun, Mercury is only visible shortly before sunrise or after sunset, and observation is further hindered by the fact that its light must pass obliquely through the lower atmosphere where it is distorted or filtered by dust and pollution. See Table at solar system.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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mercury in Culture

Mercury definition

The Roman name of Hermes, the messenger of the Greek and Roman gods.

Note: The planet nearest the sun is named Mercury. It moves swiftly in its orbit like the messenger of the gods.

Mercury definition

In astronomy, the planet closest to the sun, named after the fleet-footed messenger of the Roman gods (see under “Mythology and Folklore”) because of its swift movement in its orbit. Mercury takes only eighty-eight days to go around the sun. (See solar system.)

Note: Mercury is sometimes visible from the Earth as a morning or evening star.

mercury definition

In chemistry, a heavy, silvery metallic element, a liquid at normal temperatures. Mercury expands or contracts rapidly in response to changes in temperature and therefore was once widely used in thermometers.

Note: The term mercury is used figuratively in such expressions as “The mercury's rising” to mean that the temperature is going up.
The New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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