"the Roman god Mercury," herald and ambassador of his father, Jupiter, mid-12c., Mercurie, 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. De Vaan thinks it possible the whole stem *merk- was borrowed and the god-name with it.

Mercury later was identified with Greek Hermes and still later with Germanic Woden. From his role as a messenger and conveyor of information, since mid-17c. Mercury has been a common name for a newspaper. 

The planet closest to the sun was so called in classical Latin (c. 1300 in English). A hypothetical inhabitant of the planet was a Mercurean (1855) or a Mercurian (1755). For the metallic element, see mercury.

In U.S. numismatics, the Mercury-head dime (so called by 1941) was in circulation from 1916; properly it is the female head of Liberty, in her characteristic cap, here winged to symbolize freedom of thought. But the resemblance to Mercury was noted in coin circles at once, and the coin design sometimes was popularly mistaken as the head of Mercury, Roman god of making money and thieving, in his winged hat. It was so-called in 1933 in newspaper articles calling attention to the fasces on the reverse. The coin is more correctly the Winged Liberty-head dime (simple Liberty-head dime being a designation of the previous design). The design was replaced in 1946, which made it necessary for it to have an agreed-upon specifying name.

There's the four-year-old who counted out 20 cents with the remark: "A boy dime and a girl dime."
Translated, this means a Roosevelt dime and one classified by coin books as the "new Mercury head" dime.
[Dothan Eagle, June 25, 1951]

mercury (n.)

silver-white fluid metallic element, late 14c., from Medieval Latin mercurius, from Latin Mercurius (see Mercury). Prepared in ancient times 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 was associated with the planet 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. Compare quicksilver, which is its popular name. It has a freezing point of -39° C. The use of the word in reference to temperature or state of the atmosphere (by 1756) is from its use in thermometers and barometers.

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Definitions of Mercury from WordNet
mercury (n.)
a heavy silvery toxic univalent and bivalent metallic element; the only metal that is liquid at ordinary temperatures;
Synonyms: quicksilver / hydrargyrum / Hg / atomic number "
mercury (n.)
temperature measured by a mercury thermometer;
the mercury was falling rapidly
Mercury (n.)
(Roman mythology) messenger of Jupiter and god of commerce; counterpart of Greek Hermes;
Mercury (n.)
the smallest planet and the nearest to the sun;