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

Most microorganisms, like bacteria and yeast, are harmful, but probiotics are beneficial exceptions that contain helpful bacteria or yeast similar to those in the gut. —Ayesha Gulzar, Verywell Health, 8 Sep. 2025

Living in the mud of the North Sea were microorganisms whose genes looked a lot like ours. —Veronique Greenwood, Quanta Magazine, 8 Sep. 2025

To solve this problem, materials scientists at Nanyang Technological University in Singapore have concocted a new sunscreen recipe that spares the ocean’s vital microorganisms. —Andrew Paul, Popular Science, 4 Sep. 2025

The microorganisms living in the microbial mat feed on decaying organic material. —David Bressan, Forbes.com, 30 Aug. 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