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

Think of your gut as an ecosystem with a large community of trillions of microorganisms. —Caitlin Pagán, Verywell Health, 24 Nov. 2025

This ecosystem includes face mites, a microorganism that lives within hair follicles, as described by another display in the exhibit. —Sophia Arndt, Twin Cities, 22 Nov. 2025

Humanity has a weird alliance with a variety of opportunistically cooperative microorganisms that make some of our favorite treats. —Literary Hub, 19 Nov. 2025

Donors must be thoroughly screened and tested to protect against infectious diseases and microorganisms, for example. —Jolene Edgar, Allure, 19 Nov. 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