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

That has tipped the lake’s ecosystem out of balance, spurring the growth of microorganisms that turn shallow bays and shorelines into no-go zones. — Jonathan Mingle, ProPublica, 4 Nov. 2026

High temperatures damage key structural parts of these microorganisms, leaving them unable to multiply and cause infections. — Marlee Shaffer, The Conversation, 4 Nov. 2026

Some varieties also contain probiotics, which are beneficial live microorganisms. — Trista Chan, HEALTH, 2 Nov. 2026

The gut is lined with bacteria and other microorganisms that regulate the immune system. — Carrie Madormo, Verywell Health, 26 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