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micra

[mahy-kruh] /ˈmaɪ krə/
noun
1.
a plural of micron.

micron

[mahy-kron] /ˈmaɪ krɒn/
noun, plural microns, micra
[mahy-kruh] /ˈmaɪ krə/ (Show IPA)
1.
Also called micrometer. the millionth part of a meter. Symbol: μ, mu.
2.
Physical Chemistry. a colloidal particle whose diameter is between 0.2 and 10 microns.
3.
Physics. a very small unit of pressure, equal to that exerted by a column of mercury 1μ high.
Also, mikron.
Origin
1880-1885
1880-85; < Greek mīkrón a little, noun use of neuter singular of mīkrós small; see -on1
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for micra

micra

/ˈmaɪkrə/
noun
1.
a plural of micron

micron

/ˈmaɪkrɒn/
noun (pl) -crons, -cra (-krə)
1.
a unit of length equal to 10–6 metre. It is being replaced by the micrometre, the equivalent SI unit
Word Origin
C19: New Latin, from Greek mikros small
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 micra

micron

n.

"one millionth of a meter," 1892, coined 1880 in French from Greek mikron, neuter of mikros "small" (see mica).

Online Etymology Dictionary, © 2010 Douglas Harper
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micra in Medicine

micron mi·cron or mi·kron (mī'krŏn')
n. pl. mi·crons or mi·cra (-krə) or mi·krons or mi·kra (-krə)

Abbr. μm See micrometer.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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micra in Science
micron
  (mī'krŏn')   
See micrometer2.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Article for micra

micron

metric unit of measure for length equal to 0.00l mm, or about 0.000039 inch. Its symbol is mum. The micrometre is commonly employed to measure the thickness or diameter of microscopic objects, such as microorganisms and colloidal particles. Minute distances, as, for example, the wavelengths of infrared radiation, are also given in micrometres.

Learn more about micron with a free trial on Britannica.com
Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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