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

Inside, microorganisms break down the body into soil in a natural process that generates heat to reach temperatures of 131 F (55 C) or higher — enough to kill germs. —Dorany Pineda, Fortune, 2 May 2026

In short, this step ensures the mission doesn't accidentally carry any hitchhiking microorganisms to Mars. —Chelsea Gohd, Space.com, 1 May 2026

Inside, microorganisms break down the body into soil in a natural process that generates heat to reach temperatures of 131 F (55 C) or higher — enough to kill germs. —ABC News, 1 May 2026

Eat and Drink More Fermented Foods Fermentation is the conversion of carbohydrates to alcohol or organic acids using microorganisms—yeasts or bacteria—under anaerobic conditions. —Cynthia Sass, Health, 30 Apr. 2026

Word History

Etymology

International Scientific Vocabulary

First Known Use

1880, in the meaning defined above

Rhymes for microorganism

• activism
• ageism
• albinism
• altruism
• aneurism
• animism
• aphorism
• atomism
• barbarism
• bolshevism
• botulism
• brahmanism

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