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

When mercury reaches an aquatic environment, microorganisms like sulfate-reducing bacteria often convert it into a more toxic form of the element known as methylmercury. —Caroline Tien, SELF, 22 Apr. 2025

May Improve Gut Health The gut microbiota is a mix of microorganisms (tiny living things, including bacteria) that play a role in many body functions, such as the immune system and metabolism. —Karen Berger, Pharmd, Verywell Health, 11 Apr. 2025

While intestines may have lots of friendly microorganisms, intestines can have pathogens too. —Bruce Y. Lee, Forbes.com, 11 Apr. 2025

Cats with inflammatory bowel disease might need a prescription-strength probiotic supplement with higher amounts of microorganisms. —Bestreviews, Chicago Tribune, 4 Apr. 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