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

Using advanced fermentation, Gozen places microorganisms in 13-square-foot trays of water, and the living creatures create a lattice structure. —Carved, Sourcing Journal, 25 June 2025

During rainstorms, agricultural runoff, sewage, or decaying organic matter are pulled into the water, leading to high levels of nutrients that allow microorganisms to thrive, according to Galbadage. —Julia Ries, Health, 17 June 2025

Research suggests that the damp surfaces of an air conditioner can be breeding grounds for microorganisms like fungi. —Emily Kay Votruba, EverydayHealth.com, 16 June 2025

And Answers For Friday, May 23 Scientists are now exploring how the gut microbiome — the trillions of bacteria and other microorganisms that live in our digestive system — may influence cancer risk. —Adaira Landry, Forbes.com, 23 May 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