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micro-

  1. a combining form with the meanings “small” (microcosm; microgamete), “very small in comparison with others of its kind” (microcassette; microlith), “too small to be seen by the unaided eye” (microfossil; microorganism), “dealing with extremely minute organisms, organic structures, or quantities of a substance” (microdissection; microscope), “localized, restricted in scope or area” (microburst; microhabitat), “(of a discipline) focusing on a restricted area” (microeconomics), “containing or dealing with texts that require enlargement to be read” (microfilm; microreader), “one millionth” (microgram).
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Also especially before a vowel, micr-.

Origin of micro-

< Greek: combining form representing mīkrós small
Can be confusedmacro- micro-
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for micro-

micro-

micr-

combining form
  1. small or minutemicrospore
  2. involving the use of a microscopemicrography
  3. indicating a method or instrument for dealing with small quantitiesmicrometer
  4. (in pathology) indicating abnormal smallness or underdevelopmentmicrocephaly; microcyte Compare macro- (def. 2)
  5. denoting 10 –6microsecond Symbol: μ
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Word Origin

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

Word Origin and History for micro-

word-forming element meaning "small, microscopic; magnifying; one millionth," from Latinized comb. form of Greek mikros "small, little, petty, trivial, slight" (see mica).

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Online Etymology Dictionary, © 2010 Douglas Harper
micro- in Medicine

micro-

pref.
  1. Small:microblast.
  2. Abnormally small:microcephaly.
  3. Requiring or involving microscopy:microsurgery.
  4. One-millionth (10-6):microliter.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
micro- in Science

micro-

  1. A prefix that means: “small” (as in microorganism) or “one millionth” (as in microsecond).
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.