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litmus

[lit-muh s]
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noun
  1. a blue coloring matter obtained from certain lichens, especially Roccella tinctoria. In alkaline solution litmus turns blue, in acid solution, red: widely used as a chemical indicator.
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Origin of litmus

1495–1505; earlier lytmos < Old Norse litmosi dye-moss, equivalent to lit- color, dye + mosi moss
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for litmus

litmus

noun
  1. a soluble powder obtained from certain lichens. It turns red under acid conditions and blue under basic conditions and is used as an indicator
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Word Origin

C16: perhaps from Scandinavian; compare Old Norse litmosi, from litr dye + mosi moss
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 litmus

n.

"blue dye-stuff obtained from certain lichens," early 14c., from Middle Dutch lijkmoes (Dutch lakmoes), from lac (see lac) + moes "pulp." Another theory is that it represents Old Norse litmose, literally "lichen for dying," from Old Norse lita "to dye, to stain," from litr "color, dye" (see lit (n.1)) + mos "moss." Yet another idea connects the first element to Middle Dutch leken "to drip, leak" (see leak (v.)).

Whichever was the original word, it probably was influenced by the others. The dye is obtained from certain lichens. It is naturally blue but turns red in acid and is restored to blue by alkalis. Figurative use of litmus test is first attested 1957, from scientific use of litmus-treated paper as a chemical indicator. Litmus paper with this meaning is from 1803.

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Online Etymology Dictionary, © 2010 Douglas Harper

litmus in Medicine

litmus

(lĭtməs)
n.
  1. A water-soluble blue powder derived from lichens that changes to red with increasing acidity and to blue with increasing basicity.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

litmus in Science

litmus

[lĭtməs]
  1. A colored powder, obtained from certain lichens, that changes to red in an acid solution and to blue in an alkaline solution. Litmus is a mixture of various closely related heterocyclic organic compounds.♦ Litmus is typically added to paper to make litmus paper, which can be used to determine whether a solution is basic or acidic by dipping a strip of the paper into the solution and seeing how the paper changes color.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

litmus in Culture

litmus

[(lit-muhs)]

In chemistry, a kind of paper used to tell whether a solution is an acid or a base. Acids turn blue litmus paper red; bases turn red litmus paper blue. Other testing paper or sophisticated instruments can be used to measure the pH of a solution more precisely.

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Note

The term litmus is often used to refer to a general and simple test: “Your vote on this issue is a litmus test of your political philosophy.”
The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.