mercury

The word “mercury” means a heavy, silvery metallic element that is liquid at room temperature and highly toxic; also called quicksilver. In plain terms, a toxic liquid metal, or informally, the temperature itself.

“Mercury” is pronounced MURK-yuu-ree (/ˈmɜɹkjəɹi/ in IPA).

Here is “mercury” used in a sentence: “Old thermometers used mercury, which is why they're rarely made that way anymore.”

“Mercury” is a noun.

The word “mercury” comes from Middle English. From Middle English mercurie, ultimately named after the Roman god Mercury, likely because of the metal's quick, fluid movement.

“Mercury” is a fairly common word in modern English.

“Mercury” has 2 distinct senses listed in this dictionary. The most common is: a heavy, silvery metallic element that is liquid at room temperature and highly toxic; also called quicksilver.

Quicksilver is an older name for mercury, describing a silvery metal that is liquid at room temperature and flows readily. It uses an old sense of "quick" meaning alive or moving, because the liquid metal seems to move as if alive.

Use lowercase mercury for the metal and for the thermometer reading. Capitalise Mercury when referring to the planet or the Roman god, since those are proper nouns.

Yes. Mercury is a highly toxic element, which is why spills from broken thermometers need careful cleanup and why its use in everyday products has declined. Its toxicity is a defining fact about the metal alongside its unusual liquid state.