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

One theory is that changes in a person's gut microbiome (a collection of microorganisms that live in the gut) can affect serotonin, dopamine, and other chemical messengers in the brain known as neurotransmitters. —Gaylyn Henderson, Mph, Health, 17 Mar. 2025

This explosion of microorganisms is known as the Great Oxygenation Event (GOE) and took place around 2.5 billion years ago. —Stephanie Edwards, Discover Magazine, 10 Mar. 2025

This biodiversity means that the many different minerals and nutrients plants require will be made available by the decomposing attributes of one variety of these microorganisms or another. —Joshua Siskin, Orange County Register, 8 Mar. 2025

If the necks were pointed straight up, the broth often turned cloudy with microorganisms. —Carl Zimmer, New York Times, 17 Feb. 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