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

Every person has a unique balance of microorganisms in their digestive system within their gut microbiome.4 The microbiome influences overall health. —Amber J. Tresca, Verywell Health, 2 May 2025

More recent studies, however, analyze whole communities of microorganisms. —Ava Erickson, Outside Online, 29 Apr. 2025

About 70 feet down, the rover would see purple clumps along the lakebed formed by cyanobacteria, a microorganism that thrives in habitats like sinkholes that are high in sulfate and low in oxygen. —Emilie Le Beau Lucchesi, Discover Magazine, 18 Apr. 2025

Fermentation is a simple metabolic process in which microorganisms, such as bacteria, break down organic molecules like sugars or carbohydrates into simpler compounds. —Victoria Corless, Space.com, 15 Apr. 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