What is the meaning of Mercury?

noun

• A heavy silvery toxic univalent and bivalent metallic element; the only metal that is liquid at ordinary temperatures.
  • synonyms: quicksilver, hydrargyrum, Hg, atomic number 80
• Roman mythology. ( messenger of Jupiter and god of commerce; counterpart of Greek Hermes)
• The smallest planet and the nearest to the sun.
• Temperature measured by a mercury thermometer.
  • usage: "the mercury was falling rapidly"