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

Example Sentences

Recent Examples on the Web The broth is piped to the colony’s anaerobic digester, where microorganisms break down biodegradable waste to produce methane gas that will fuel spacecraft and other vehicles. Joe Pappalardo, Popular Mechanics, 8 May 2023 Swimming pool water, with adequate chlorine disinfection levels and pH maintenance, is much less likely to contain infectious microorganisms and so represents a much safer environment for recreational swimming. Primrose Freestone, CNN, 17 Apr. 2023 That's because freezing prevents the growth of the microorganisms that cause foodborne illness. Sheena Chihak, Better Homes & Gardens, 13 Apr. 2023 And, as with mosquitoes, that tick spit sometimes carries hitchhiking microorganisms that cause debilitating diseases in humans. John Sass, Field & Stream, 11 Apr. 2023 In a study published last week in Nature Ecology & Evolution, researchers found seabirds that had ingested more microplastics had more disease-causing and antibiotic-resistant microorganisms in their guts. Will Sullivan, Smithsonian Magazine, 6 Apr. 2023 More beach vacation ideas Elafonisi Beach, Elafonisi, Greece Just off the coast of Crete lies Elafonisi, a small island known for pink sands created by colorful microorganisms and pieces of coral. Steven Casale, Travel + Leisure, 3 Apr. 2023 This makes people drink water containing dangerous microorganisms that negatively affect their pancreas and cause cravings for sugar and carbs. Discover Magazine, 29 Mar. 2023 But now microorganisms are being used to boost that process and unlock new revenue streams for farmers. Jamie Hailstone, Forbes, 16 Mar. 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'microorganism.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


International Scientific Vocabulary

First Known Use

1880, in the meaning defined above

Time Traveler
The first known use of microorganism was in 1880

Dictionary Entries Near microorganism

Cite this Entry

“Microorganism.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/microorganism. Accessed 8 Jun. 2023.

Kids Definition


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


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

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