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

Using microorganisms to remove environmental pollutants is not a new concept. — Catherine Armbruster, The Conversation, 17 Sep. 2026

The fermentation process also reduces kefir’s lactose content because its microorganisms consume some of the milk sugar. — Daryl Austin, USA Today, 16 Sep. 2026

Discoloration can happen when microorganisms grow or when the food’s natural chemicals start to break down. — Julie Marks, Verywell Health, 16 Sep. 2026

Higher ear humidity could lead to changes in your ear microbiome, or the collection of microorganisms that live in your ear canal, Nieman said. — Julia Landwehr, HEALTH, 14 Sep. 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