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[mag-nee-zhuh, -shuh] /mægˈni ʒə, -ʃə/
a white, tasteless substance, magnesium oxide, MgO, used in medicine as an antacid and laxative.
Compare milk of magnesia.
Origin of magnesia
1350-1400; Middle English: philosophers' stone < Medieval Latin magnēsia < Greek () Magnēsía (líthos) (the stone) of Magnesia; sense development obscure
Related forms
magnesian, adjective


[mag-nee-shee-uh, -zhee-uh] /mægˈni ʃi ə, -ʒi ə/
ancient name of Manisa. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for magnesia


another name for magnesium oxide
Derived Forms
magnesian, magnesic (mæɡˈniːsɪk), magnesial, adjective
Word Origin
C14: via Medieval Latin from Greek Magnēsia, of Magnēs ancient mineral-rich region
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
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Word Origin and History for magnesia

late 14c., in alchemy, "main ingredient of the philosopher's stone," from Medieval Latin magnesia, from Greek (he) Magnesia (lithos) "the lodestone," literally "(the) Magnesian (stone)," from Magnesia, region in Thessaly, which is said to be named for the native people name Magnetes, which is of unknown origin. The ancient word, in this sense, has evolved into magnet. But in ancient times the same word, magnes, was used of lodestone as well as of a mineral commonly used in bleaching glass (modern pyrolusite, or manganese dioxide).

In Middle Ages there was some attempt to distinguish lodestone as magnes (masc.) and pyrolusite as magnesia (fem.). Meanwhile, in 18c., a white powder (magnesium carbonate) used as a cosmetic and toothpaste was sold in Rome as magnesia alba ("white magnesia"). It was from this, in 1808, that Davy isolated magnesium. He wanted to call it magnium, to stay as far as possible from the confused word magnesia, but the name was adopted in the form magnesium. Meanwhile from 16c. the other name of pyrolusite had been corrupted to manganese, and when, in 1774, a new element was isolated from it, it came to be called manganese.

Magnesia in its main modern sense of "magnesium oxide" (1755) is perhaps an independent formation from Latin magnes carneus "flesh-magnet" (c.1550), so called because it adheres strongly to the lips.

Online Etymology Dictionary, © 2010 Douglas Harper
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magnesia in Medicine

magnesia mag·ne·sia (māg-nē'zhə, -shə)
Magnesium oxide.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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magnesia in Science
A white powder with a very high melting point. It is used to make heat-resistant materials, electrical insulators, cements, fertilizer, and plastics. It is also used in medicine as an antacid and laxative. Chemical formula: MgO.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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