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

This can introduce impurities or harmful microorganisms to the bathroom environment as a result. —Ethan Stone, USA Today, 15 Mar. 2026

In your intestines, colonies of microorganisms (bacteria, fungi, viruses, and others) make up the gut microbiome. —Mark Gurarie, Verywell Health, 12 Mar. 2026

Beneficial soil microorganisms start to die off. —Brandee Gruener, Southern Living, 10 Mar. 2026

Although a lot of plants prefer or need nutrient-rich soils to reach their full potential, there are plenty of plants that flourish in what is considered poor or low-quality soil—generally defined as soil lacking in nutrients and microorganisms. —Lauren David, Martha Stewart, 9 Mar. 2026

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