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

As Hamshaw explains it, the microorganisms used to make tempeh produce enzymes that begin breaking soybean proteins into smaller components during fermentation, including peptides and amino acids. — Alessandra Signorelli, Vogue, 25 Sep. 2026

The core technology behind much of this process is anaerobic digestion, in which microorganisms break down organic material in an oxygen-free environment. — Kaif Shaikh, Interesting Engineering, 22 Sep. 2026

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

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