• 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

Related Words

microorganism, germ, virus, bug, bacterium, bacillus, pathogen, microbe, parasite, illness, ailment, sickness, disease, infection, egg, unit, plague, antibody, crud, embryo

Examples from the Web for micro-organism

Historical Examples

  • A micro-organism is a parasite when it can live in animal tissues.

    Essays In Pastoral Medicine

    Austin Malley

  • The micro-organism is found in the secretions from the mouth, throat, or nose, and in particles of detached membrane.

    Health on the Farm

    H. F. Harris

  • Altogether there are many obscure points about this micro-organism, which is apt to assume a puzzling variety of forms.

  • There are many kinds of fermentation, each with its own special form of minute plant life or micro-organism.

    A Practical Physiology

    Albert F. Blaisdell

  • The micro-organism of small-pox and that of cancer (the existence of which is assumed) have not yet been isolated.

British Dictionary definitions for micro-organism


  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

Word Origin and History for micro-organism


also microorganism, 1855, from micro- + organism.

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Online Etymology Dictionary, © 2010 Douglas Harper

micro-organism 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.

micro-organism 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.