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

Experts at Eurac Research found that Ötzi's remains still contain a complex community of ancient and modern microorganisms — offering a rare glimpse into the microbial past of early humans. —Andrea Margolis, FOXNews.com, 22 June 2026

Research shows a higher diversity of microorganisms can be one indicator. —Will Stone, NPR, 22 June 2026

Scientists now also know that Legionella pneumophila is just one of dozens of species of microorganisms that can cause respiratory illness from airborne water particles. —Robert Promisloff, The Conversation, 19 June 2026

These foods — from yogurt to sauerkraut to kimchi and kefir — are made with microorganisms that transform them. —Anahad O’Connor, Washington Post, 17 June 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