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

Biologics are derived from natural sources, such as human or animal genes and microorganisms, and are designed to block specific immune system proteins that cause inflammation. —New Atlas, 7 Oct. 2025

Gut Benefits of Probiotics Your GI tract is full of microorganisms, some good and some bad. —Kirstyn Hill, Health, 6 Oct. 2025

In a mouse study, maple syrup improved the gut microbiome (the community of microorganisms in the digestive tract) and acts similarly to prebiotics, which help the good bacteria in your gut flourish. —Brittany Lubeck, Verywell Health, 29 Sep. 2025

But prebiotic supplements help feed those microorganisms. —Bestreviews, Mercury News, 24 Sep. 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