microorganism

noun

mi·​cro·​or·​gan·​ism ˌmī-krō-ˈȯr-gə-ˌni-zəm 

: an organism (such as a bacterium or protozoan) of microscopic or ultramicroscopic size

Examples of microorganism in a Sentence

Recent Examples on the Web

The agency said the disinfectants carried labels that made unverified claims about their ability to kill microorganisms. —Rey Covarrubias Jr, AZCentral.com, 9 Dec. 2025

Living inside of all of our intestines is a bevy of bustling natural bacteria and other microorganisms working together called the gut microbiome. —Laura Baisas, Popular Science, 3 Dec. 2025

Think of your gut as an ecosystem with a large community of trillions of microorganisms. —Caitlin Pagán, Verywell Health, 24 Nov. 2025

This ecosystem includes face mites, a microorganism that lives within hair follicles, as described by another display in the exhibit. —Sophia Arndt, Twin Cities, 22 Nov. 2025

Word History

Etymology

International Scientific Vocabulary

First Known Use

1880, in the meaning defined above

Rhymes for microorganism

• absolutism
• adventurism
• aestheticism
• africanism
• agnosticism
• alcoholism
• anabolism
• anachronism
• anglicanism
• antagonism
• arianism
• asceticism

Kids Definition

microorganism

noun

mi·​cro·​or·​gan·​ism ˌmī-krō-ˈȯr-gə-ˌniz-əm 

: 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 

: an organism of microscopic or ultramicroscopic size