• synonyms


[mahy-kroh-awr-guh-niz-uh m]
See more synonyms for microorganism on Thesaurus.com
  1. any organism too small to be viewed by the unaided eye, as bacteria, protozoa, and some fungi and algae.
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Origin of microorganism

First recorded in 1875–80; micro- + organism
Related formsmi·cro·or·gan·ic [mahy-kroh-awr-gan-ik] /ˌmaɪ kroʊ ɔrˈgæn ɪk/, mi·cro·or·gan·is·mal, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for microorganisms

Contemporary Examples

Historical Examples

  • All such very small plants and animals are known as microorganisms.

    General Science

    Bertha M. Clark

  • The diseases resulting from the microorganisms are not contagious and do not spread by contact of diseased with healthy animals.

    House Rats and Mice

    David E. Lantz

  • The virulence is not great enough to kill a sufficiently high percentage of rats that eat food containing the microorganisms.

    House Rats and Mice

    David E. Lantz

  • However, very few experiments have been performed to determine the importance, if any, of these microorganisms to the host.

  • The passage of microorganisms through the digestive tract of Blaberus craniifer mounted under controlled conditions.

British Dictionary definitions for microorganisms


  1. any organism, such as a bacterium, protozoan, or virus, of microscopic size
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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

microorganisms in Medicine


  1. An organism of microscopic or submicroscopic size, especially a bacterium or protozoan.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

microorganisms in Science


  1. An organism that can be seen only with the aid of a microscope and that typically consists of only a single cell. Microorganisms include bacteria, protozoans, and certain algae and fungi. See Note at germ.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

microorganisms in Culture


Organisms so small that they can be seen only through a microscope. (See bacteria, protozoa, and viruses.)

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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.