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

In humans, the term often refers to the microorganisms living in or on a specific body part, such as the skin or gastrointestinal tract. — Hanna Wickes, Kansas City Star, 5 Oct. 2026

In collaboration with Hegemann in the early 2000s, Nagel helped identify proteins known as channelrhodopsins, light-sensitive ion channels that allow for rapid responses to light in certain microorganisms. — Encyclopedia Britannica, 5 Oct. 2026

The agency also said an investigation found no laboratory incident involving pathogenic microorganisms. — Efrat Lachter, FOXNews.com, 5 Oct. 2026

Hale begins his long list of mud’s wonders with the chemical functions of microorganisms in mud. — Matthew Wills, JSTOR Daily, 5 Oct. 2026

Word History

Etymology

International Scientific Vocabulary

First Known Use

1880, in the meaning defined above

Rhymes for microorganism

• activism
• albinism
• altruism
• aneurism
• animism
• aphorism
• atomism
• barbarism
• bolshevism
• botulism
• brahmanism
• calvinism

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