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 sediments also contained elevated calcium, calcite, and sulfur signatures linked to microorganisms adapted to warmer environments. —Kaif Shaikh, Interesting Engineering, 25 May 2026

Traditional compost piles use aerobic microorganisms to decompose plant materials. —Mary Marlowe Leverette, Southern Living, 24 May 2026

Yogurt is one of the most accessible sources of probiotics, the live microorganisms that support gut health. —Samantha Agate, Miami Herald, 23 May 2026

This is because, during fermentation, helpful microbes can develop, and when consumed, these bacteria may help support the complex ecosystem of microorganisms living in the digestive tract, known as the gut microbiome. —Daryl Austin, USA Today, 23 May 2026

Word History

Etymology

International Scientific Vocabulary

First Known Use

1880, in the meaning defined above

Rhymes for microorganism

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

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