[ mahy-kroh-awr-guh-niz-uhm ]
See 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.

Origin of microorganism

First recorded in 1875–80; micro- + organism

Other words from microorganism

  • mi·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. 2023

How to use microorganism in a sentence

  • There are other infective diseases, in which we have not yet found the causative micro-organism, but we presume its existence.

  • We do not know the cause of yellow fever despite the claims of Sanarelli that he has isolated the specific micro-organism.

  • This test is that it cannot be infected again for a long time, if at all, by the same micro-organism.

    Darwinism and Race Progress | John Berry Haycraft
  • This he also proved to be caused by a minute form of life, and that fowl cholera is due to still another form of micro-organism.

  • If I can keep the specific micro-organism that causes hog-cholera off my place, I need not fear the disease.

    The Fat of the Land | John Williams Streeter

British Dictionary definitions for microorganism


/ (ˌmaɪkrəʊˈɔːɡəˌnɪzəm) /

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

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

Scientific definitions for microorganism


[ mī′krō-ôrgə-nĭz′əm ]

  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.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.