[mag-nee-zee-uh m, -zhuh m, -shee-uh m]
noun Chemistry.
  1. a light, ductile, silver-white, metallic element that burns with a dazzling white light, used in lightweight alloys, flares, fireworks, in the manufacture of flashbulbs, optical mirrors, and precision instruments, and as a zinc substitute in batteries. Symbol: Mg; atomic weight: 24.312; atomic number: 12; specific gravity: 1.74 at 20°C.

Origin of magnesium

From New Latin, dating back to 1800–10; see origin at magnesia, -ium Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for magnesium


  1. a light silvery-white metallic element of the alkaline earth series that burns with an intense white flame, occurring principally in magnesite, dolomite, and carnallite: used in light structural alloys, flashbulbs, flares, and fireworks. Symbol: Mg; atomic no: 12; atomic wt: 24.3050; valency: 2; relative density: 1.738; melting pt: 650°C; boiling pt: 1090°C

Word Origin for magnesium

C19: New Latin, from magnesia
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for magnesium

silvery-white metallic element, 1808, coined by English chemist Sir Humphrey Davy (1778-1829) from white magnesia (q.v.), in which it was found, + chemical ending -ium.

Online Etymology Dictionary, © 2010 Douglas Harper

magnesium in Medicine


[măg-nēzē-əm, -zhəm]
n. Symbol Mg
  1. A light metallic element that burns with a brilliant white flame, used in various analgesic, antiseptic, anticonvulsant, and antacid pharmaceuticals. Atomic number 12.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

magnesium in Science


  1. A lightweight, moderately hard, silvery-white metallic element of the alkaline-earth group that burns with an intense white flame. It is an essential component of chlorophyll and is used in lightweight alloys, flash photography, and fireworks. Atomic number 12; atomic weight 24.305; melting point 649°C; boiling point 1,090°C; specific gravity 1.74 (at 20°C); valence 2. See Periodic Table.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.