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

These microorganisms are the base of a unique food chain that supports a community of cave-dwelling organisms. —Humberto Basilio, Scientific American, 7 Nov. 2025

Probiotics Probiotics are living microorganisms that can support gut health. —Merve Ceylan, Health, 7 Nov. 2025

The garden uses restorative agricultural practices to prevent topsoil erosion by enriching the soil with microorganisms, Carlson said. —Nollyanne Delacruz, Mercury News, 29 Oct. 2025

The activity and makeup of these microorganisms are called the microbiota, which can affect human health. —Karen Berger, Verywell Health, 27 Oct. 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