microorganism

noun

mi·​cro·​or·​gan·​ism ˌmī-krō-ˈȯr-gə-ˌni-zəm How to pronounce microorganism (audio)
: an organism (such as a bacterium or protozoan) of microscopic or ultramicroscopic size

Examples of microorganism in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Allison Wells, a senior instruction specialist in Purdue University’s Department of Food Science, said in a Campus Insights Media video that the starter’s microorganisms begin breaking down starches and other larger components in the dough. — Ryan Brennan, Miami Herald, 20 Oct. 2026 Allison Wells, a senior instruction specialist in Purdue University’s Department of Food Science, explained in a Campus Insights Media video that the starter’s microorganisms begin breaking down starches and other larger components in the dough. — Ryan Brennan, Kansas City Star, 20 Oct. 2026 Manure adds nutrients, microorganisms break it down, the pasture recovers and the chickens later return to healthier ground. — Ryan Brennan, Fort Worth Star-Telegram, 17 Oct. 2026 In the human intestine, microorganisms are concentrated mainly in a mucus layer near the villi’s surface. — Neetika Walter, Interesting Engineering, 15 Oct. 2026 See All Example Sentences for microorganism

Word History

Etymology

International Scientific Vocabulary

First Known Use

1880, in the meaning defined above

Time Traveler
The first known use of microorganism was in 1880

Rhymes for microorganism

See All Rhymes for microorganism

Browse Nearby Words

micronutrient
microorganism
micropaleontological
See all Nearby Words

Cite this Entry

“Microorganism.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/microorganism. Accessed 27 Oct. 2026.

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Kids Definition

microorganism

noun
mi·​cro·​or·​gan·​ism ˌmī-krō-ˈȯr-gə-ˌniz-əm How to pronounce microorganism (audio)
: an organism (as a bacterium) of microscopic or less than microscopic size

Medical Definition

microorganism

noun
mi·​cro·​or·​gan·​ism -ˈȯr-gə-ˌniz-əm How to pronounce microorganism (audio)
: an organism of microscopic or ultramicroscopic size

More from Merriam-Webster on microorganism

Britannica.com: Encyclopedia article about microorganism

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